Mike375 suggested that some rifle shoot better with the shoulder pushed back about .004".

An old 7mm Mauser I aquired recently shot quite well with many moa groups while the brass was fire forming. Since it's chamber takes a .004" shim and closes on a no go gage it has some headspace.

Recently the groups went to 2 moa and became all horizontal.

I did as Mike suggested and pushed the shoulders back and now it's shooting round groups about MOA again!

Your chamber may be banana shaped, or your neck die could be off, like mine was. The resulting rounds will be off, and inaccurate. Get a concentricity gauge and see which of the two is the culprit.

I am FL sizing and was leaving tension on the bolt as it closes. This also helped to keep the bolt closed as the safety does not lock it.

I have a concentricity gage but the problem seems to be solved.

What did your runout before vs. after?

A fired case, measured at the expansion web, is about five tenths out of round.

Runout of a fired case measured near the end of it's neck is .001", Fl sized it's .002" and a loaded round averages .003" measured 1/10 of an inch from the neck.

Savage99, Years ago I discovered that pushing the shoulder back about .003 Improved accuracy tremendously...I know lots of great shooters neck size only and they say they get great accuracy.......It just doesn't work for me....I'm shooting some 6mm BR rifles, .223 Ackleys and all have custom barrels and chambers....Maybe they are banana shaped but my cases come out of the chamber straight..I know that the bench rest boys say they bump the shoulder about .100 but I know for a fact that some of the very best B/R shooters bump the shoulder more that .001 (about .0025 to .003) It sure works for me and it doesn't seem to shorten the life of the brass...Good luck....George

99, that's a sweet little rifle... details?

With my Savage lever action in .308Win. I didn't have much choice since it required my using small base dies. I think most lever actions and semi-autos are like this. Best wishes.

Cal - Montreal

quote:

Originally posted by Savage99:
I am FL sizing and was leaving tension on the bolt as it closes.

Savage99, on page 6 of this section there was an extensive discussion titled "How many of you use Neck Sizing Dies vs. Partial Resizing" that goes into great detail on this. From this I think that if you have tension on the bolt then you are still neck sizing and have not gone through partial full length resizing to get to full length resizing yet. In summary of the above mentioned post - when the die first contacts the CASE at the pressure ring it pushes the shoulder forward (the case then becomes hard to chamber), it then continues to resize the case body until the die contacts the shoulder. Just before the point where the die contacts the shoulder and pushes it back (the case becomes easy to chamber), that is partial full length resizing. Full length resizing is where the case shoulder is pushed back far enough so the case is no longer compressed between shoulder and bolt face.

As a reult of the above mentioned post, I got a Redding bushing die and a Lee Collett die to try neck sizing but gave it up and went back to partial full length resizing in FL die when concentricity went to hell.

Maybe if we could lure Hot Core and Idaho Shooter back into another discussion we could have another spirited discussion!!

Could it be that bolt pressure distorts the case and causes additional misalignment?

quote:

Originally posted by Savage99:
Since it's chamber takes a .004" shim and closes on a no go gage it has some headspace.

Could you explain this to me, must confess I'm not familiar with it.

I wish Mike375 would step in now and give us the link while filling in some details. Pushing the shoulder back to improve accuracy is a new idea to me. Previously I just varied things and sometimes got lucky. Not knowing that it might be an important variable however means that I might introduce a change in the FL die and spoil a good load in the past.

I don't wish to get into a discussion of case sizing semantics but to just dwell on pushing the shouder back. Is it for instance the best way most of the time?

quote:

Originally posted by woods:

quote:

Originally posted by Savage99:
Since it's chamber takes a .004" shim and closes on a no go gage it has some headspace.

Could you explain this to me, must confess I'm not familiar with it.

Woods,

I am using Foster no go gages as it's the opinion of many that a chamber that will accept one is still serviceable and then some. My standard is .005" over the no go gage as maximum.

I put the no go gage into the chamber and then drop a small coupon of shim onto it while holding the muzzle down. Most beverage cans range around .004" and are easy to cut with a sizzors.

Brad,

It's a 1950 Brno 21h in 7-57. The standard double set trigger had been replaced by the single stage trigger shown and it has an old pad on it. I am new to these superb rifles and have learned much here about them from our resident experts. There are a number of excellent threads here in the archives.

Everyone who has seen it really is obsessed with these rifles. While CT has been a gun manufacturing haven and a wealthy one at that since the founding of this country there are many here in this state who have not seen that model nor it's full stocked 22f.

My favorite story so far about it is that a AR member from AK was passing thru CT and he met me at the range. This guy has hunted all over the world and owns more guns than I do. After shooting some of my nice M70's etc I pulled out the battered old Brno which looks like something that Finn Aagaard dragged thru the thorns for a lifetime.

He says "I am taking this rifle with me"! I did not know him all that well and he starts walking around the parking lot with it (nobody else was there and the bolt was open) talking to himself! Finally he calms down and hands it back to me. You know the rush we get when we pick up some gun that we want.

The scope shown on it is the very old Weaver K4 that has parallax at all ranges. It's been replaced by a Leu 3-9 Compact which is about the only scope that would fit due to bolt clearance problems, the express sights on the barrel and the long 5.5" ring separation.

Here is what it should look like with the original triggers.


Thanks for your interest.

Cutting through all the BS and numbers, the point is it worked for you, all else is unimportant...

Howeverm, I notice that you are shooting a Mod 21 Brno and it has a exceptionally long throat and any tendency towards a round sitting off center in the chamber is magnafied greatly...for what its worth.

Then why the horizontal groups? I am interested in why but a universal "cure" would be so easy.

The out of round chamber may also be a 3 to 9 o'clock situation.

99, I figured it was a Brno 21... I've always wanted one, particularly with a mannlicher stock... Great rifle!

Thanks,

BA

I went to the range today with my 22-250 and duplicated the above mentioned phenomenon. I used virgin and twice fired/ necksized brass. I got 1 hole groups with the virgin brass and my pet load, and a vertical sting and much lower pressures with the twice-fired stuff.

Here is Mike375's post from 24hr.

"In bench style guns from 270 through to 358 STA that had been chambered with JGS reamers I found full length sizing so as to have about .003" to .004" headspace was the most accurate.

When I had barrels done I had the gunsmith chamber them so there was about .003 or .004 headspace on new brass. As general rule I was able to get the same point of impact with new and full sized fired cases.

What I also found in general was that full sized with the approx .003 head space shot better with the bullets further off the rifling as compared to neck sizing.

As a side note, because of the great accuracy and general loading flexibility of the 358 STA we tried an experiment.

Barrels of what we call Number 5m about .72" at 26 inches were done in 338 Win, 340 Wby with both 1 in 10 and 1 in 12 and without Wby freebore and also 375 H&H.

The 358 STA was the best. HOWEVER, the barrels were 1 in 14 and undersize at .357. The particular barrel maker in Australia had a feeling that undersize barrels were bettter and in 35 he made .356 .357 and .358

The 358 STAs also worked extremely well with Barnes X bullets.

This barrel make and another make a lot of barrels for what we call full bore target shooting, which is 308 and out to 900 yards. For the 144 grain boat tail they find a .3065 barrel is best. A mate of mine had a 300 Jarret made on both the .3065 and .308 barrel and the .3065 was better with Barnes Xs.

The 358 STAs were so accurate and with just about anything that went bang they became a little cult calibre amoung a few Australians. They were all very accurate.

Whether it was the .357 barrels, the particular JGS reamer or particular batch of RCBS dies we will never know.

Lastly, one of the 358s with Number 5 barrel was bedded into a Remington Rubber stock that comes with the Stainless Rem 700, a wood stock that had been a 416 Remington and both bedded and done as glue in with recoil and as a glue in without recoil lug into an aluminium bench stock we have in Australia.

The best acccuracy came from the Remington rubber stock.

Mike