Hi,

I went to the range to test some loads in my .270 Winchester this weekend.

The results were somewhat perplexing/confusing.
I had worked loads up to 49.8 gr (of S365 [+/- IMR4350]) in the past, and I had experience no pressure problems. I only recently got my Chrony so I am not sure what velocity these previous loads were yielding.

Using this as a point of departure, I loaded up some ammo as below. All loads using S365 (+/- IMR4350).

No. Charge Powder Vel. Desc.
1 49.8 S365 2632 Hornady InterLock SP
2 49.8 S365 2625 Rhino
3 50.3 S365 2792 Hornady InterLock SP ***
4 50.3 S365 2651 Rhino
5 50.8 S365 2708 Rhino ***

[*** == SIgns of high pressue]

The start loads of 49.8 gr (#1 & #2) delivered good accuracy in both the Hornady & Rhino, but velocity is on the low side.
I then tried three of the 50.3/Hornady loads (#3). Extraction was sticky on the first two, and I had to use my palm to hit the bolt open after the third shot. The group was also blown out.

I stopped (testing) the Hornady loads there.

The Rhinos were fine using 50.3 gr of S365, but signs of pressure (sticky extraction) were displayed after firing one round from #5 (50.8 gr S365).

Note that I was seeing signs of high pressure a full 1 grain BELOW the Somchem maximum load (51.3 gr) for S365 & 150 grain bullets.

Now, for the questions;

1) Is this unusual; High pressures displayed, with relatively low velocity delivered.

2) I presume that if want to try and achieve 2,800 fps using 150 grain bullets in my .270, I should try a slower powder such as S385 (+/- MRP)?
3) Rhinos seem to produce lower pressures (and velocity) compared to Hornady Interlocks. Is this possibly due to the Rhinos' Moly coating?

4) I should mention that this rifle is new. I have only put about 100 rounds through the barrel. Could performance improve as the barrel is "worn in"?

Appreciate your comments.

Cheers

1) Perhaps not usual, but many of us have seen it.

2) Yes, IMR4350 will usually not give the fastest velocities for the 150 grain bullets. Try IMR4831, H4831 or IMR7828 or equivalents.

3) This is usual with moly coatings, lower bore friction means lower pressures, and lower velocities.

4) You haven't told us anything meaningful about the rifle. If the bore is rough then more shooting may help a little. If it is a custom barrel then not much difference.


.

Thanks for the info.

The rifle is a new Zastava (Mark X).

I presume you are talking about loads for 150gr bullets. I have found the following:

50.0gr S365 Lot 139 - 150 Hornardy Interbond - Fed 215 (magnum) Primer 2930fps in 26" Ferlach Barrel - SD=2.8fps. 150gr Nosler Ballistic tips has given me the same velocity.

49.6gr S365 Lot 112 - 150 Hornady Interbond - Hirtenberg (Hotest Magnum Primer) giving my similar accuracy and same impact on 100 meters. Did not test velocity here.

Both these loads above has given me 3 shots cutting one another on the target.

However, the max load for lot no 112 is indicated as 53.0gr and the max load for lot 139 is indicated as 51.3gr. I would suggest you check the lot number and verify it with Somchem. Please also check AOL etc.

S385 did not yield better results = 56.0gr Lot 008 09_2006 gave me 2855fps with 18.4 SD. My opinion is that S365 is a better choice. Try to identify the reason for the high pressure and try to manage that. Maybe try another brand of primer and work the load up. If the barrel is shorter it would also yield lower velocities. However, speed is not everything. 100fps would not make a difference as long as you hit the target. Bucks would not know the difference between a bullet coming at 2800fp or 2900fps. Just enjoy your reloading!

Thanks for the data, and advice!

Cheers

quote:

Originally posted by umshiniwam:
Thanks for the info.

The rifle is a new Zastava (Mark X).

Sorry, I should add that it has a 24" barrel.

You say you've loaded this before without issues, but the info is a bit thin.

With what bullet?

Same cases?

Same powder lot number?

Be sure that the seating depths are not too long, i.e. that you aren't jamming the bullets into the lands.

Did you measure the case length? If the case is too long you can be pinching the bullet into the case as the case mouth jams into the leade area of the throat. This will increase pressure.

Are these new cases? If so try fireformed cases and see what happens. Start a little lower and see what happens as you come up.

If you have excessive headspace with new cases you may get pressure signs incorrectly. Still you need to take notice of these things, particularly hard bolt lift so you do need to worry!

Reloader 270, Somchem no longer lists lot numbers in the manuals. Where are you seeing the difference in the data?

quote:

Originally posted by ARWL:
You say you've loaded this before without issues, but the info is a bit thin.

Loaded up to 49.8 gr previously, but did not chrony these results.

This time I started at 49.8 gr (knowling that was the last safe load that I had tested) and hit pressure signs at 50.3 gr.

I used PMP large rifle magnum primers.

quote:

With what bullet?

Hornady Interlock SP 150 gr

quote:

Same cases?

Yes, I have only fire new Winchester cases in this rifle (I have only put 50 rounds through the barrel previously)
Plus the dozeon or so shot on the weekend. It is a new rifle.

quote:

Same powder lot number?

Yes, Somchem S365, lot 059 (06/2010).

quote:

Be sure that the seating depths are not too long, i.e. that you aren't jamming the bullets into the lands.

I was cautious of this, and seated the bullets 3mm+ from the lands.

quote:

Did you measure the case length? If the case is too long you can be pinching the bullet into the case as the case mouth jams into the leade area of the throat. This will increase pressure.

As these are new cases, I did not. Should one check new cases in any event?

quote:

Are these new cases? If so try fireformed cases and see what happens. Start a little lower and see what happens as you come up.

Thanks, will try this!

quote:

If you have excessive headspace with new cases you may get pressure signs incorrectly. Still you need to take notice of these things, particularly hard bolt lift so you do need to worry!

Bolt lift was okay, but extraction very sticky, so I was definitely "tickling the dragon's tummy" as they say.

quote:

Reloader 270, Somchem no longer lists lot numbers in the manuals. Where are you seeing the difference in the data?

I also have not seen any various data published for different lots (not for a long time). If there is a variance between lots, then Somchem should be making this data available via their (non-existant at the moment) web site.

Cheers!

Do you have any Hodgdon H4831? I was getting 2,805 from my 270 Winchester BRNO ZKK 600 with Hornandy 150 grain Interlock and no pressure issues here in England. Using standard CCI (non-magnum) primers.

Hi

quote:

Originally posted by enfieldspares:
Do you have any Hodgdon H4831? I was getting 2,805 from my 270 Winchester BRNO ZKK 600 with Hornandy 150 grain Interlock and no pressure issues here in England. Using standard CCI (non-magnum) primers.

We have Somchem S361 which has a similar burn rate, give or take 5%.

I might give that a try.

Cheers

The issue you describe is exactly why I DON'T use a chronograph in load work-up. The sign you got of hard extraction is that of excess pressure irrespective of what the velocity is.

It's also the usual thing for maximum obtainable velocity at reasonable pressure levels to be different with different powders. In addition, it's entirely to be expected that two supposedly identical rifles shooting the same load will give significantly different velocities. Velocity is only an indirect measure of pressure and isn't consistent which is why I don't find it useful as a pressure sign.

quote:

Originally posted by Grumulkin:
The issue you describe is exactly why I DON'T use a chronograph in load work-up. The sign you got of hard extraction is that of excess pressure irrespective of what the velocity is.

It's also the usual thing for maximum obtainable velocity at reasonable pressure levels to be different with different powders. In addition, it's entirely to be expected that two supposedly identical rifles shooting the same load will give significantly different velocities. Velocity is only an indirect measure of pressure and isn't consistent which is why I don't find it useful as a pressure sign.

Agree 100% that one should not se velocity as an indicator of pressure. This I have now seen for myself.

A question; How do ammunition manufacturers load cartridges that will give a reasonable predictable velocity (and safe pressure)in various firearms?

quote:

How do ammunition manufacturers load cartridges that will give a reasonable predictable velocity (and safe pressure)in various firearms?

Easy, they control the process; in many instances non-canister (their own blend) of powder, propritary primers, ect.

quote:

The issue you describe is exactly why I DON'T use a chronograph in load work-up.

I agree w/grum 100%.

I think you've been given some great advice above.

There's certainly other powders available and they work, too but I'ma sorta H-4831SC Guy when it comes to the .270 Winchester with both 130 & 150 grain bullets (don't load the 140's).

I'd suggest trying whatever Somchem offers that is close in buring rate to H-4831SC; you say it's S361, that's where I'd go.

Also, I wouldn't get too fired up about seating bullets too close to the lands with hunting ammo. I'd check reliable magazine length initially and go from there. If I can get some extra O.A.L. out of the magazine without playing with the lands; that would be my starting length.

For hunting ammo I prefer reliability as my main criteria, followed by velocity within (#3 priority) reasonable hunting accuracy (to me, 1.5 M.O.A., if it's better, then good).

Should be a good bullet purchase, an O.A.L. that operates through the magazine & doesn't get close enough to the lands to get me into trouble.

I'd also reco checking your case length.

quote:

The rifle is a new Zastava (Mark X).

Did you give the bore an extra good scrub to ensure all the "new" rifle gunk is outa the barrel?

Good Luck with your 270 Win. loading.

Let's come at this from an entirely different direction.

I had a new chrony, Oehler. We were wildcatting some .223 Ackley and I was getting close to 4,000 fps. getting flattened primers. Also, I had some +P loads in 45 ACP which were reading velocities way below the Hodgdon load data.

Then I moved the chrony screens farther down range. I'd been reading unburned powder and muzzle blast.

I could never understand how people could shoot their screens. Yeah, well . . . at point blank range it's easy to shoot through the window. At functional distances, shooting the screens gets to be a bit more of a risk.

Maybe the difference in bullet construction affected the pressures.

quote:

Originally posted by umshiniwam:
A question; How do ammunition manufacturers load cartridges that will give a reasonable predictable velocity (and safe pressure)in various firearms?

They do it just like we should but have the advantage of having pressure measuring equipment. They test a load to see what gives optimal accuracy and record velocities and pressures; then they publish their data.

As you peruse data, you will notice that loads with different powders come up with different velocities and that the pressures for "maximum loads" in the published loads are different. Even if you had pressure measuring equipment and got your load to the exact pressure of factory loads, it wouldn't necessarily be the best load for your gun.

The various ammunition manufacturers also keep their loads conservative enough that even in a worst case scenario of a tight chamber, short throat, etc., their ammunition won't wreck a gun or a shooter.

For what it's worth, this is what I do:

1. I start in the lower third of the published load and make batches of cartridges each incrementally increasing the load for each batch.

2. I shoot groups off the bench with each batch and record group sizes. Generally, loads with lower charges will give larger groups which will tighten to a degree as the loads are increased. There will come a point at which the group sizes will start to widen again. I stop where the groups are tightest.

Obviously, if you experience hard extraction, blown primers or other signs of excess pressure, you stop load workup there and decrease the load a bit. At that point, if you're not satisfied with the velocity or accuracy, you need to try a different powder, primer and/or bullet.

Thanks for all of the great advice guys!

umshiniwam:

I have been loading the 270 Winchester since the late 1960's. It is my favorite cartridge and I own several. Most of my loads are either IMR4350, or IMR4831, although I really like Accurate 3100 with the 150 grain bullet, I have reached velocities of 3,000, with a 150 Nosler and a 26" barrel with 3100 and Accurate's suggested max load, and nice tight groups. I wish I had some experience with the powders you are using, but I don't, and can't offer anything there. However, I find that with some of my loads, they are too hot in Remington brass, and fine in Winchester, especially during the hot Arizona summers. I'd make sure you are NOT on the lands with your bullets, and maybe try a differnt brand of brass.

I find that the 270 Winchester is a very easy round to load for, and in my experience, if I stayed within the powder manufacturer's guidlines I never had any pressure problems.

Jerry

[/QUOTE]
We have Somchem S361 which has a similar burn rate, give or take 5%.

I might give that a try.

Cheers[/QUOTE]

Please just remember S361 is a ball powder and that you need to use a proper magnum primer with it. Loading with ball powder could give a double detonation in very low temperatures and could be dangerous. Try to get Hirtenberg Primers or use Federal 215 (magnum) primers.

MRP is our Reloader 22 which is a very good powder for 150 gr bullets. Having a 24" barrel helps too. Unless youhave a particularly slow barrel, you should be able to approach or slightly exceed 3000 fps at maximum loading. That max number varies from 56 to 59 grains in different data tables so I'd start a little below 56 and work up.

quote:

Originally posted by Reloader270:

quote:

We have Somchem S361 which has a similar burn rate, give or take 5%.

I might give that a try.

Cheers

Please just remember S361 is a ball powder and that you need to use a proper magnum primer with it. Loading with ball powder could give a double detonation in very low temperatures and could be dangerous. Try to get Hirtenberg Primers or use Federal 215 (magnum) primers.

Thanks for that valuable advice!

I'll rather try S385 then.

Cheers!

I am sure you already know all this, so I am not saying it to "enlighten" you...just to give you a bit of moral support and perhaps a reminder...

Velocity, though interesting, is not a good basis for choosing a load. Safety, consistency, and predictable down range performance (like accuracy) are. 100 fps more or less velocity won't mean squat in the game fields if you are familiar with your rifle's trajectory...and you should make it a point to become familiar with the trajectory with any load you use to shoot at other living beings. It is just the humane thing to do.

If you are loading around "maximum" levels for your rifle, the change of ANY component can change the safe load for your gun. That includes bullet make, weight, materials, etc. It also includes powder lot #s.

Loading data velocities in ANY COMPANY'S powder manual are usually optimistic for most guns actually used in the field. Load data is at best a set of useful generalized guidelines. At worst it is sometimes just a sales tool bordering on hype.

It is DEFINITELY NOT a scientific formula developed for YOUR gun. That's why everyone needs to "work-up" their own data. And the safest approach is to start low and work UP to safe, reliable, useful loads, NOT to start high and work DOWN to them.

Best wishes and good luck with your .270...it's a good plains game cartridge the world over.

Thanks for the words Alberta.

I am usually not a guy who chases velocity, but in this case I would like to try and get 2,850 fps from my .270 with 150 grain bullets. Reason being that I am booked to hunt black wildebeest in teh Free State in a couple of weeks, and I have been advised by the farmer that shots of 250 to 300 yards should be expected.

The little bit of extra velocity will help with down range energy (read bullet momentum, as I am not a follower of kinetic energy == killing power school of thought.)

This would give it a slight advantage over using my .30-06 with 180 grain loads.

My load development experience has served as a reminder to be cautious when working up loads, and as you say, each rifle is individual and must have loads tailored for it.

I am also surprised that article authors publish their load data. It makes for interesting reading but any load other than the minimum starting load is actually useless information.

Thanks for the wise words.

You are most welcome.

Another suggestion, which MAY make you feel a bit better about your good loads which you have already developed and have in hand is this:

Take the velocity of the loads you have, and the velocity you want, and run "drop charts" on them from the muzzle to 400 yards. Bet you'll find there isn't more than about an inch or two difference in drop all the way out to 400.

From my hunting experiences, an inch or two better trajectory is no noticieable difference at all when doing field shooting.

As to killing effect, the better accuracy and consistency of your best load will count a great deal more than any slight difference in hitting power. You get the bullet into that 8-12" quick-kill zone at 300 yards and they will die right now!!

quote:

Originally posted by Alberta Canuck:

From my hunting experiences, an inch or two better trajectory is no noticieable difference at all when doing field shooting.

Too true!

So I did some more experimenting at the range yesterday...

I appreciate (and agree with) the comments about accuracy being paramount over velcoity, but I am pursuing this as an experiment and learning experience.

I tried 150 grain (Hornady Interlock SP) loads again, this time using S385 which is the slowest-burning extruded powder available from Somchem (+/- Norma MRP).

Somchem booklet states 52 (2,579 ft/s) to 57 (2,848 ft/s) grains S385 for .270 Winchester with 150 grain bullets. I started at 52, loaded 3 x loads in increasing increments of 1 grain.

The results were slightly better than previously, but I still am almost 200 ft/s below the velocity which I am hoping to achieve (+/- 2,850 ft/s)

(c) = charge
(v) = velocity

c v v/c
==================
52 2437 46.9
53 2521 47.6
54 2575 47.7
55 2661 48.4
56 2728 48.7 *** Sticky extraction

Cases are Winchester, PMP LRM primers

I also tried some 130 grain loads, also Hornady Interlock SP but using S365 which is +/- IMR4350.

Somchem booklet states 50.4 (2,631 ft/s) to 54 (3,114 ft/s) grains S365 for .270 Winchester with 130 grain bullets. I started at 50.4, loaded 3 x loads in increasing increments of 1 grain.


The results were also below expected.

c v v/c
=====================
50.4 2609 51.8
51 2635 51.7
52 2658 51.1
53 2723 51.4
54 2765 51.2 *** Sticky extraction

Cases are Winchester, PMP LRM primers

Now for the questions;
1) The only alternative powder left to tr is S361, which has a similar burn rate to S385 (which I have tried with teh 150 grainers as per above). However S361 is a ball powder. Is it possible that the ball powder might perform better than the extruded owder or can I expect similar results?

2) Could I achieve desired velocity by changing bullet brand? The Hornady Interlock SP doe not seem to have excessive bearing surface, so I am dubious about this.

3) Will any given rifle (with the right powder & component combination) deliver advertised factory ammunition velocities, or do some rifles just not perform to these standards, in which case I have such a rifle?

Last one is more a request for opinion:

4) Somchem give "v/c Factor" figures for their loads, whcih is velocity / charge. They suggest that this should be used to gauge if your "system" is operatng at higher or lower pressure than the system used to determice the laod tables. The v/c factors which I am calculating are below those that they give, which would suggest that my system is operating at lower pressures, yet I am still seeing signs of pressure at the maximum loads. This is contrary to what they suggest should be the case.

So what should I try next?

1) Ball powder?
2) Chaneg primer (I have aquired soem CCi 250 primers)
3) So far I have only been using new cases. Perhaps I should try using once-fired cases.

Will any of these display a marked in increase in velocity?

Cheers

umshiniwam:

You tried S365, with a 130 grain bullet. As you stated this powder is like IMR4350 +-. I am shooting 56 Grains of IMR4350/130 Nosler Ballistic Tip/3075+fps, and no pressure signs or extraction problems. If in fact S365 is a IMR4350 clone, in my Winchester Model 70, your loads would be rather light.

I have a couple other questions now: Can you please mic, (measure) the cartridges, as they come out of your sizing die, make a note, and then do the same after a cartridge is fired. Lets look for a chamber problem. Also, hows the barrel? Has it been shot a lot, is it rough? There is always an answer, if the problem is mechanical. Now if the powder is mislabeled thats another issue. If you have your bullets seated a little off the lands, that won't create a problem, too close is another story. Lets look at some of the questions I have asked, and see if here is a solution there.

Your questions.

1. I see no advantage to using a ball powder over an extruded, in this case other than for loading speed. In my 270's I have not had better results with ball powders.

2.The bullet, if it is sized to the bore correctly won't be a significant problem, and I seriously doubt, you could gain nearly 400fps by changing bullets.

3. I find my 270's are fairly close to the reloading manual's numbers. I also find once in a while, a rifle, that is fast or slow, by up to about 200fps. Of course here we are assuming the rifle(s) are in good condition.

4. I think until you find and solve the problem, this is premature.

Also, how about head space? Have you tried just neck sized brass?

I don't know what else I can send along.

Regards

Jerry

Hi Jerry.

Thanks for you considered response.

quote:

You tried S365, with a 130 grain bullet. As you stated this powder is like IMR4350 +-. I am shooting 56 Grains of IMR4350/130 Nosler Ballistic Tip/3075+fps, and no pressure signs or extraction problems. If in fact S365 is a IMR4350 clone, in my Winchester Model 70, your loads would be rather light.

This is what has be puzzled!

I have used S365 (+/- IMR4350) for the 130 gr loads and I have used S385 (+/- H4831) for my 150 gr loads.

Looking at Gerard Schultz's burn rate chart GS Custom burn rate chart (which I believe is very accuarte) the burn rates for the above comparisons are almost identical.

From the research that I have done, it is unusual to run into pressure problems with either of these powders, given that they are both slow burners. (I read somewhere of H4831: 'Just fill the case with powder and stick a bullet in it' which I'll admit was probably an exageration, but it makes a point.)

I am using powder from the same can of S365 in my .30-06 (which is also a brand new Zastava Mauser) and I have yet to find any signs of pressure at max advised Somchem loads for that powder with 180 grain bullets in the rifle.

So this adds to my confusion.

quote:

Can you please mic, (measure) the cartridges, as they come out of your sizing die, make a note, and then do the same after a cartridge is fired.

Will do. I have just (last night) full-length resized 50 once-fired cases. I'll measure them before firing. I should measure the head diameter?

quote:

Also, hows the barrel? Has it been shot a lot, is it rough

The rifle is a brand new Zastava Mauser. Barrel has now fired exactly 94 rounds.

quote:

Now if the powder is mislabeled thats another issue

I don't believe so, as I have been achieving expected results from the same canister in my .30-06 (also a brand new Zastava, fired 18 rounds). There has apparently been a dubious batch of S365 produced recently (Lot 061) but this canister is not from that batch.

quote:

If you have your bullets seated a little off the lands, that won't create a problem, too close is another story

I have seated the bullets to the cannelure. COL is 81 mm. (Both 130 gr & 150 gr loads)

quote:

Also, how about head space? Have you tried just neck sized brass?

Being a new rifle, I'm not sure if this could be the problem. The Zastava (Mark X) is a "cheapie" but is a fairly well-made one. Not out of the question though. I have not tried neck-sized brass. I should perhaps invest in a neck-sizing die.

quote:

I don't know what else I can send along.

You have been more than helpful. Appreciate it!

Cheers,
Scott.

It is always possible to get a lot of soft brass which would show pressure signs prematurely. I've had that happen twice in 30 years, once with Norma and once with Remington brass. (Three if you count Bertram but it is ALWAYS soft in my experience). Is this a new previously untried batch of brass? Since you say the same can of powdwer doesn't act as badly in your 30-06, I'm leaning toward a brass issue.

quote:

Originally posted by tiggertate:
I'm leaning toward a brass issue.

Interesting point that you make.

The brass in Winchester brass, 2 separate bags of 50 pcs each. These two bags were bought separately, but at the same dealer and within the space of about two months.

Something that I recall now, the primer pockets were noticeably tight. I use a Lee hand primer, and I have primed plenty of new brass before. These required noticeably more force to prime than I had previously noted when priming new brass.

Something else that I did (but I did with the same to the .30-06 brass as well) is ream the flash holes with a Lyman flash hole uniformer. It did not seem to affect the '06 performance though.

I also notice that 16 out of the 50 .270 Winchester cases that I re-sized (for the first time) last night had dents in their necks, as you would normally find when using too much lube. I also found this odd, as I did not lube these more than I have lubed any other cases in the past, and I very seldom get these dents. Could this be an indicator of soft brass as well?


Cheers & thanks for the input.
Scott.

Hi

A photograph of primers increasing charge from left to right.

Does teh far right one look flattened?

quote:

Originally posted by umshiniwam:
Hi

A photograph of primers increasing charge from left to right.

Does teh far right one look flattened?

Both right side cases look like flat primers to me. But they look like they could be from either headspace or pressure. Are those circular impressions on the second from the right from the bolt face tool marks?

Tigger makes a point about the bright marks on the one fired case. But looking at them, they look ok in comparison to mine.

Lets solve the brass issue, run a 30-06 into your full length 270 die, load and fire it, then check the results. the 30-06 is about .050 shorter than the 270, but it's not a big deal for this test. The other thing you can do, is back off the sizing die about a 1/8 to 1/4 turn on your press. This accomplishes "partial" full lenght resizing, and dosen't move the shoulder. You can keep the relationship of shoulder to the bolt face at a minimum this way. Also, wipe any lube off the shoulder of your case before sizing, this will solve the dent issue, no lube is necessary on the shoulder anyway, and also check to make sure the relief hole in the die is clear.

Regards

Jerry

Hi Jerry

quote:

Originally posted by Jerry Eden:
Can you please mic, (measure) the cartridges, as they come out of your sizing die, make a note, and then do the same after a cartridge is fired. Lets look for a chamber problem.

I went to the range today, things went friom bad to worse.

I tried the following changes.

1) Switch from magnum primers to CCI 200
2) Seat the bullet a little (1.5 mm) further out, but still away from the lands. The idea here was tyo try and increase internal volume and reduce pressure.

I only fired three shots, 1 x 130 gr load and 2 x 150 g loads. For two of these I had the use a cleaning rod to fore the bolt open, and the thid one (a 15 0gr Rhino bullet) I could just manage to get the bolt open.

Obviosuly I was heading into dangerous territory, so I stopped it just there.

The loads were

130 gr Hornady SP, CCI 200 primer, 53 gr S365, vel. 2818 ft/s
150 gr Hornady SP, CCI 200 primer, 55 gr S385, vel. 2735 ft/s
150 gr Rhino SS, CCI 200 primer, 55 gr S365, vel. 2755 ft/s

But to answer your question;

I took the measurements just up from the rim, where a line forms in the brass.

I measured the head diameter of a new case, and a 1 x fired and full length resized case. Both were 11.75 mm in diameter.

Then I measured the same diameter of the three cases fired today; 12.05 mm, 12.04 mm & 12.04 mm. +/- 0.3 mm difference.

Some random measurements on once fired .270 brass all shows a diameter of between 11.99 & 12.06 mm, mostly 12.04 mm.

As a control I measured the same dimension on some fired .30-06 brass and these were all exactly 11.89 mm.

Could this be a headspace issue?

Cheers,
Scott.

The three cases from cartridges fired today.





Cheers

Your last 3 primers look pretty flat.
Especially the one on the right.
Notice the junction of the primer face and the firing pin dent has almost no radius!!!

The bulge after firing is about twice what I like so I would consider your chamber a bit big and sloppy. It is about as bad as a Lee-Enfield chamber or a Jap 6.5 Type 38. Both are notorious for having chambers much larger than the brass - the chambers are about .010 to .012 inch larger than new unfired brass and the both provide a huge bulge like your chamber does.

Umshiniwam: Looking at the 2 cases in the pic you posted, the primers look more LOW pressure to me than high. My fired cartridges:the primers fill up the little gaps near the head of the case.

As to headspace, we would need an OAL measurement before and after. Is it possiblle for you to get a little IMR4350, load 55 or 56 grains, with a 130 grain bullet, and see what happens? I have a particular rifle, a 243, that I have had rebarreld, and it is giving me fits. I may just change barrels and be done with it, but I am told by the smith, it is a Shilen and should be a tack driver. Who knows, frustrating at best.

Jerry

As long as you are not measuring CHE & PRE, you will never know what the Pressure is actually doing.

Best of luck to you.

Thanks Hot Core, I'll give that a try. I'll need to ge capable measuring instruments first.

It seems like a sensible next step would be to fire some factory loaded ammunition through the chrony, and see what that reveals.

Cheers

quote:

Originally posted by umshiniwam:
Thanks Hot Core, I'll give that a try. I'll need to ge capable measuring instruments first.

It seems like a sensible next step would be to fire some factory loaded ammunition through the chrony, and see what that reveals.

Cheers

Just spotted your other post. As you have seen, a Chronograph often provides more "confusion and misleading info" than it does usable Data.

But. once you fire the Factory cartridges, you can use it to establish your Benchmark Standard " if " you measure the PRE as outlines in the above link.