I have an Alexander Arms AR-15 in 6.5 Grendel that's giving me fits.

Using Alexander Arms load data I started out with 120gr Ballistic Tips and TAC. AA data list 27.5 Start and 28.8 Max with a max velocity of 2560fps/24 in barrel and an OAL of 2.245. I started at 27.5 and blew the primer, my velocity (16 in) was 2214fps.

Thinking it might be my TAC, I gathered more load data from Hodgdon, Ramshot and Accurate.

Accurate list 2230 at 23.6 to 26.3 with a max pressure of 51,900psi. I loaded 24, 25 and 26gr with BTs. 24gr looked OK, but at 25gr ( 1.6gr below max) I have some serious extractor marks.

Ramshot lists X-T at 25.1 to 27.9gr max with a max pressure at 51,970psi. I loaded 25, 26 and 27gr with BTs. Again 25 looked OK, 26 ( 1.9gr below max) showed some serious extractor marks.

Then I tried Hodgdon 322. Same thing, serious extractor marks 1.6gr below max.

Thinking this may be a result of the Nolser BT I tried it all again with a 120gr Speer HC. My results were the same, very high pressure signs at loads well below max.

So, what the hell is going on with this rifle that I would have such high pressure signs like this? It is my understanding that blown primers. loose primer pockets, and extractor marks don't show up until around 70-75,000psi. 20k over pressure with a less than minimum charge just don't seem right to me.

Any Ideas?

Perhaps your brass is a trifle soft? The usual pressure signs are normally fairly good indicators IF the brass is of normal hardness, but soft brass will give pressure signs early. How about trying brass from a different manufacturer?

Also in the area of brass, I've encountered both too-thick necks and 'the dreaded doughnut' in new brass from some sources in other chamberings, it might be worth your while to check your neck dimensions. Try to insert an unfired bullet into the unsized neck of a fired case. If the bullet slips all the way down through with no felt resistance at all, then things are probably OK with your neck dimensions. If you feel any slight resistance at all, then it's time to investigate the necks further.
Regards, Joe

May be completely off base here as I am not familiar w/the 6.5 Grendel. Can't help but wonder about case length in your chamber since you are getting much higher pressures than one would expect w/loads you are using.

Could you have some cases that are a tad too long for your chamber, thus not allowing expansion of neck to release bullet?

Have had a couple of match chambers that were very sensitive to case length.

Regards,
hm

quote:

Originally posted by hm1996:
May be completely off base here as I am not familiar w/the 6.5 Grendel. Can't help but wonder about case length in your chamber since you are getting much higher pressures than one would expect w/loads you are using.

Could you have some cases that are a tad too long for your chamber, thus not allowing expansion of neck to release bullet?

Have had a couple of match chambers that were very sensitive to case length.

Regards,
hm

Brass is trimmed to trim to length.

Hey Steve, Try to get a measurement of the "Groove Diameter" at the muzzle with a pair of 0.001" capable Calipers.

If the number of grooves or the muzzle configuration won't allow this, try sticking the tip of a 6.5mm Bullet into the muzzle and turning it so the Lands cut a light groove. Then do the same with another 6.5mm rifle and see if the diameters are close to the same.

If you do not have another 6.5mm rifle handy, call a Gun Shop and go where they have one.

I'm wondering if they accidently got a 6mm Barrel into the 6.5mm batch.
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One other thing to try is to determine the actual distance to the Lands. If it is short Throated, that can cause the Pressure to be Higher than normal. I use the old faithful Cleaning Rod Method which should be somewhere in that link.
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I happen to have a rifle that shows Pressure Indications before reaching the MAX Loads shown in all the Manuals. At first it concerned me until I focused on the Groups. It is one of the most accurate Belted Mags I've ever owned.

Didn't bother to check velocity for a long time, but eventually did when comparing B-Tips and Partitions. It is close enough to the regular velocity that it just dosen't concern me at all.
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J.D.Steele might be correct. If you can get a different Brand of Cases to try, it could be that simple.

Do you have to Form the 6.5 Grendel cases from a different Case?

quote:

One other thing to try is to determine the actual distance to the Lands. If it is short Throated, that can cause the Pressure to be Higher than normal. I use the old faithful Cleaning Rod Method which should be somewhere in that link.

This chamber has what Bill Alexander (Alexander Arms) calls a "Compound Throat". Bullets seated to just about any length will come in contact with some rifling.

quote:

Originally posted by Hot Core:
...If the number of grooves or the muzzle configuration won't allow this, try sticking the tip of a 6.5mm Bullet into the muzzle and turning it so the Lands cut a light groove. Then do the same with another 6.5mm rifle and see if the Bore diameters are close to the same.

Edit in: Bore

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quote:

Posted by Steve:
This chamber has what Bill Alexander (Alexander Arms) calls a "Compound Throat". Bullets seated to just about any length will come in contact with some rifling.

Hey Steve, I'm an Engineer and do not see how that is possible. Do you have any details that would explain that claim.

I'm always willing to learn something new.
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By the way, it might be worth asking Mr. Alexander about the High Pressure Indicators, since he has apparently done something a bit different to the Lead than what is considered typical.

Best of luck to you.

/

Steve, Have you tried to seat a bullet into a fired BUT NOT RESIZED case? I think that the possibility of a short chamber may be an issue with your early pressure signs. Also I would ask how accurate your powder scale is, and have you verified that part of this situation. As you know, there is a cause... you just have to find it. Good luck and good shooting.

quote:

Originally posted by 308Sako:
Steve, Have you tried to seat a bullet into a fired BUT NOT RESIZED case?

Also I would ask how accurate your powder scale is, and have you verified that part of this situation. .

Yes, I have inserted a bullet into a fired case. It slides in with ease and I do not feel a dough-nut.

Powder charges are dumped with a Lyman 1200 II and double checked on a RCBS 505.

Thanks.

Alf,
It is spelled "leade" in English, is it "leed" in Afrikaans?

R

quote:

Some use the term LEAD angle, Leade angle and LEED angle...... who is right who is wrong?

Well, LEAD spells 'ledd' as in plumbate.

Any idea where the spelling, 'LEADE' came from?

For a long time I puzzled over 'mould' and 'mold' and which was which, then it turned out to be 'mould' if you were British and 'mold' if you were American!

/

quote:

Originally posted by steve4102:
...Using Alexander Arms load data I started out with 120gr Ballistic Tips ... and an OAL of 2.245. ...This chamber has what Bill Alexander (Alexander Arms) calls a "Compound Throat". Bullets seated to just about any length will come in contact with some rifling.

Hey Steve, I've given this a good bit of additional thought and do not see any advantage at all to a "Compound Throat".

The weasel words "just about any" religate this to a marketing ploy in my mind. If there was any real advantage to a unique Lead Shape, all the manufacturers would be doing it.

The real bad part about it, is it gives a person the impression there is nothing to gain by varying the Seating Depth. Any of the experienced reloaders on the Board can verify that adjusting the Seating Depth, as a final step in Load Development, can result in a good Load becoming a great Load.

After you get your High Pressure issues sorted out here is something you might find of interest. If you have not tried it before, I'll mention you might find a good many advantages by shifting from OAL/OCL to ODL for your Seating. It sure simplifies Seating the Bullet any distance off-of or into the Lead you desire.

Best of luck to you.

Update!

Here is what Bill Alexander says about his "Compound Throat".

“Ogives run from 6 diameters to 19 diameters,” Alexander said. “We had to figure out how to make guns shoot the huge diversity of bullets. We did this with a compound throat. It replaces the traditional free-bore and throat angle with a series of differing throat geometries, three different angles. It fools the bullets into thinking they are all jumping the same distance to the lands.”

http://www.gunsandhunting.com/6.5Grendel.html

Since my last post on this POS I have done a few things. I sent the gun back to Bill Alexander for him to examine and find my pressure problem. He had the rifle for almost 2 months. He said he took measurements of the chamber, throat, barrel, bore, gas system, you name it, he measured it and everything checked out perfectly. He test fired it with one factory Wolf round and one AA round. He said he found no pressure signs with factory ammo.

Since then I have been testing powders and bullets. I have tried Lapua, AA and Wolf brass. I have found no difference in brass except the Wolf has such a thin neck my Forster die will not size it down properly.

I have used load data from Hodgdon, Ramshot, Accurate, Alexander Arms and Quickload. In every case high pressure signs rear their ugly head well below max loads.
This rifle has a 16in barrel. With a 120gr bullet I should be able to get somewhere in the vicinity of 2300fps before I start blowing primers etc. No such luck.

No matter what I do, brass, bullets, powder OAL, this is what my brass looks like. In many cases with starting loads.

I know this is fireformed IMI 7.62x39 brass. I do not use it any more as the case capacity is less than true Grendel brass. I just posted this photo to illustrate what I am seeing.

So, looking at the photo, what do you estimate the pressure of these rounds?

quote:

Originally posted by steve4102:
I have an Alexander Arms AR-15 in 6.5 Grendel that's giving me fits.

Using Alexander Arms load data I started out with 120gr Ballistic Tips and TAC. AA data list 27.5 Start and 28.8 Max with a max velocity of 2560fps/24 in barrel and an OAL of 2.245. I started at 27.5 and blew the primer, my velocity (16 in) was 2214fps.

Thinking it might be my TAC, I gathered more load data from Hodgdon, Ramshot and Accurate.

Accurate list 2230 at 23.6 to 26.3 with a max pressure of 51,900psi. I loaded 24, 25 and 26gr with BTs. 24gr looked OK, but at 25gr ( 1.6gr below max) I have some serious extractor marks.

Ramshot lists X-T at 25.1 to 27.9gr max with a max pressure at 51,970psi. I loaded 25, 26 and 27gr with BTs. Again 25 looked OK, 26 ( 1.9gr below max) showed some serious extractor marks.

Then I tried Hodgdon 322. Same thing, serious extractor marks 1.6gr below max.

Thinking this may be a result of the Nolser BT I tried it all again with a 120gr Speer HC. My results were the same, very high pressure signs at loads well below max.

So, what the hell is going on with this rifle that I would have such high pressure signs like this? It is my understanding that blown primers. loose primer pockets, and extractor marks don't show up until around 70-75,000psi. 20k over pressure with a less than minimum charge just don't seem right to me.

Any Ideas?

Have you checked your scale to make sure it is working right?

quote:

Originally posted by SR4759:


Have you checked your scale to make sure it is working right?

Yes, as stated above, charges are dumped with a Lyman 1200 and double checked with a RCBS 505. Also, like most of you, when I go to the range I take several rifles and handguns. Out of the dozens of firearms I load for this is the only one giving me pressure problems.

quote:

Originally posted by steve4102:
He test fired it with one factory Wolf round and one AA round. He said he found no pressure signs with factory ammo. ...

Seems as if he didn't want to Test much ammo in it.

Anyway, if it were me, I'd try a box of the Factory Ammo myself to see what happens. Plus, I'd be using CHE/PRE to determine at what level the Pressure is too high to continue adding Powder. Just because the Manuals claim a specific Load combination will produce a Safe Velocity of XX00fps, doesn't mean every rifle will. It doesn't make me happy when it happens either.

Best of luck to you.

You don't say whether or not this is a new rifle or if you have tried any different bullets. If you don't have the tools to accurately check the bore and throat size (as well a the bullet) I suggest taking it to a gunsmith and get a quick measurement of both. Looks like something is a bit tight and I would suggest not firing it again until you get some measurements taken.

F. Prefect

quote:

Originally posted by fprefect:
You don't say whether or not this is a new rifle or if you have tried any different bullets. If you don't have the tools to accurately check the bore and throat size (as well a the bullet) I suggest taking it to a gunsmith and get a quick measurement of both. Looks like something is a bit tight and I would suggest not firing it again until you get some measurements taken.

F. Prefect

Yes it was new in Jan 09. As stated above I have been testing several powders and bullets and Bill Alexander (Rifle maker) has checked all the measurement and everything checked out.

quote:

Originally posted by Hot Core:

Just because the Manuals claim a specific Load combination will produce a Safe Velocity of XX00fps, doesn't mean every rifle will.

.

Yeh I know. It just seems as though this is an extreme situation. I have always been under the impression that pressure signs like the ones above appear somewhere in the vicinity of 70K psi. I'm getting these with Min. charges or just a hair above.

For example, Hodgdon data for the 123gr Sierra HPBT/ 322 starts with 24gr at 36,600psi and ends with 26.6gr at 49,900psi. Working my way up I got brass that looked like above at 24.8gr. How is it possible to get pressure in excess of 70K with such a light load. The max psi for this round is around 50K. If I'm getting 70K signs at low to mid range loads then my start loads should be well above 50K as well.

Hey steve, I believe I remember seeing someone above suggesting the specific "Lot" of Cases you are using might be a bit Soft in the Case Head. I do not remember ever using any IMI Cases, so I have no experience with them.

Get some Remington or Winchester Cases and try them. Perhaps your IMI Cases are faking you out. Or buy a box of Factory ammo, shoot half, pull the other Bullets, load them with your current Starting Loads and compare.

Generally speaking, something like this turns out to be something real simple we just overlook.

Best of luck to you.

quote:

Originally posted by Hot Core:
Hey steve, I believe I remember seeing someone above suggesting the specific "Lot" of Cases you are using might be a bit Soft in the Case Head. I do not remember ever using any IMI Cases, so I have no experience with them.

Get some Remington or Winchester Cases and try them. Perhaps your IMI Cases are faking you out. Or buy a box of Factory ammo, shoot half, pull the other Bullets, load them with your current Starting Loads and compare.

Generally speaking, something like this turns out to be something real simple we just overlook.

Best of luck to you.

The IMI brass was just an experiment. As ststed above, I no longer use it as it has less case capacity then true Grendel brass. There are only 3 types of true Grendel brass, Lapua, Alexander Arms(Lapua) and Wolf. My results are the same with all three.

I'm not familiar with the "dimensions" of your Case. Is there a Rem or Win Case you could Neck-Up or Neck-Down, trim and then try?

Of course, if the Factory Ammo works fine, then it could just be the "wrong" Powder for your reloading. Pulling hafe and comparing them with the Factory stuff will prove it one way or the other.

I'm out of ideas. Maybe it is good Trading Bait.

Here is a chamber cast of this so called "Compound Throat". Anyone else think this looks like it may be missing something? Like. maybe some freebore?

From looking at that chamber cast, it appears that the compound throat is actually a variety of lengths to the lands for each land. The one on top looks like it is right at the chamber, while the one above it looks further away from the chamber. I suspect this is giving you pressure signs just like a bullet jammed into the lands on a max charge. Did your 'smith see the chamber cast? This is interesting, and I would like to see what you resolve from this.

quote:

Originally posted by Bear Kodiak:
From looking at that chamber cast, it appears that the compound throat is actually a variety of lengths to the lands for each land. The one on top looks like it is right at the chamber, while the one above it looks further away from the chamber. .

No it's just hard to see in this photo. All the lands start right at the case mouth.

The Swiss seem to get by with little to no leade in their K-31's. Have you measured the chamber cast at the rifling area? Is it 6 or 6.5mm? best-o-luck

quote:

Originally posted by lonniemike:
The Swiss seem to get by with little to no leade in their K-31's. Have you measured the chamber cast at the rifling area? Is it 6 or 6.5mm? best-o-luck

6.5