Low power loads cases shortening

Match Director

linoww posted this 31 May 2025

i load 30-06 with low pressure plainbase breech seated. When I notice the primer backing out a bit I lube the case and it let's the case drive back to the breech face.Since I use the same case over and over I often just let it stay lightly lubed.

"if it was easy we'd let women do it" don't tell my wife I said that!

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Backofthehill posted this 31 May 2025

Thanks! Does the shoulder get blown back out to the correct headspace?

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Spindrift posted this 31 May 2025

One trick you can use, is to expand the necks to a larger caliber. And then, size the cases with a well-adjusted FL sizer. This will create a small "false shoulder" at the base of the neck, on which the cartridge can head-space.

I have a .30-06 with an overly long chamber, the bolt will close on a no-go gauge. When making brass for it, I expand the necks with an 8mm expander, before FL-sizing with a die adjusted to the chamber. Works fine.

When making brass for the .35 Whelen, I expand the necks to .375 before FL-sizing, to ensure correct head space from the get-go.

An affordable and flexible option for expander dies is available. The Lee universal decapping die will also accept the Lee easy-X decapping/expander mandels made for their FL dies. These mandrels are available separately, and can easily be honed down to desired diameter.

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Backofthehill posted this 31 May 2025

Thanks! That's the old remedy I forgot about. Will work up an expander in the lathe.

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CBA Member

Larry Gibson posted this 31 May 2025

It's not the firing pin that drives the cases forward in the chamber setting the shoulder back creating short case headspace. It is the power of the primer in the primer pocket especially in push feed actions. a strong ejector in the bolt face also exacerbates the problem. You can alleviate the problem by drilling out the flash holes. It is not "dangerous" and does not increase pressures. Full power loads can be used w/o any problems.

Also, "the load" will not generate sufficient pressure to blow the shoulder back out after the false shoulder is made. A full powered cast bullet load is needed such as 28 - 30 gr of 4895 w/Dacron filler under a 170 - 200 gr cast bullet.

Drilling flash holes larger;

I shoot many thousands of squib loads in various calibers but mostly in .30s. Many of these are rimless cartridges; 30-06, .308, .308 CBC, 7.65, 7.62x39 etc. The squib loads I shoot most often is a Lee 314-90-SWC-TL over 2.7 to 3.2 gr of Bullseye depending on the cartridge. Velocity is around 800 – 875 fps. I found a long time ago the shoulders do in fact get set back with light loads such as those. This is especially the case with push feed actions having the ejector in the bolt face. Case shoulder set back with such loads also occurs in CRF (Controlled Round Feed) actions but only to the extent where the extractor stops holding the case back for positive ignition. With many cast loads that use normal weight bullets in the 1600 to 2000 fps range there was little setback. It basically is a matter of the psi the load generates. It takes roughly 7,000 psi (depends on thickness and hardness of the brass along with how much the case needs to reach the chamber walls.

Measurements of shoulder set back or increase are easily taken with a Stoney Point tool. There have been basically the two theories regarding the cause; the firing pin blow theory and the primer theory. I ran the same tests with a fire formed case and inert primers; headspace was not changed. I then used the same fire formed case with live primers. In as little as two firings there was a measurable decrease in headspace. After five live primers the fired primer was noticeably backed out after firing. NOTE: this increase in headspace was with case taking LR primers. I never experience the problem with the .222 Rem or the 5.56 NATO.

Using #d drills I gradually increased the flash hole diameter with a progressively larger drill. Using a different fire formed case with each larger drill and firing 5 primers I then measured the headspace before firing and after. As the size of the flash hole increased the headspace decrease lessoned. With a # 29 drill I no longer got any decrease in headspace. I dedicated five .308 cases and five 30-06 cases that were well fire formed to their respective rifles chambers and drilled the flash holes with the #29 drill. Over the next few days I fired 50 shots with each case. There was an indoor 50” range where I was stationed so it wasn’t all that bad. After the 50 firings there was negligible change in headspace with any of the five cases of each cartridge.

The results of my test firmly demonstrated to me that it was the force of the primer explosion that drove the case forward and set back the shoulder. The squib load does not have the pressure to expand the case out to fit the chamber. By drilling out the flash hole the force of the explosion mostly went directly into the case as there is little rim left to contain it. Two other side benefits that were unforeseen; the extreme spread and standard deviations of the velocity readings improved and the case position sensitivity of the small charge was greatly reduced.

As a result of the above tests I dedicated fire formed cases for squib loads for each rifle in rimless cases and drill out the flash holes. I have fired them many, many times now with no further change in headspace. Besides the squib load mentioned I also use 311316 (# may be wrong but it’s the 118 gr GC 32-20 bullet) with Unique in the above cartridges loaded to 1400 fps or so for a little more powerful small game load. The flash hole drilled cases work just fine for those. I now use the flash hole drilled cases for all my rimless cartridges with squib and most cast bullet loads.

Further extensive pressure testing in the .308W with full powered jacketed loads demonstrated there are no pressure problems associated with the drilled out flash holes.

For drilling out the flash holes in large rifle/pistol primer pockets I recommend the use of a #28 drill.

LMG

Concealment is not cover.........

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Premod70 posted this 31 May 2025

Loading a low pressure load in a rimless case is about as dangerous as it gets in the reloading world. A rimless case relies on a balanced primer to powder pressure to keep things stable and in reality the fired case was never meant to be reloaded in the first place. Better to play with rimmed cases when starting out in reloading as the rim controls the growth pattern rather than relying on a rimless shoulder whose control on headspace is subject to many variables. Larry Gibson is correct about drilling out the flash hole but do so before firing a low pressure load in a rimless case. Drilling out a case is not a fix all rather a preventative measure that should be applied at the first loading. Good luck on your efforts.

Dale Flinchum

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Backofthehill posted this 31 May 2025

Thank you everyone! Got the 8mm expander ordered and will pull out the wire gauge drill bits.

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CBA Member

Ken Campbell Iowa posted this 31 May 2025

a couple years ago with a spiffy new 35 Whelen I had just built for a friend.

thought I would introduce him to the joys of plinking with such a Grizzly Demolisher ..

not having any factory 35W handy, we annealed lightly a dozen 30-06 brass and loaded some 200 gr cast and 10 gr 700X to fireform and bust a few pop cans.

hey... 1 inch at 50 yards fireforming !! .. Shilen barrels tend to do that for you ...

reload ... shoot ... reload ...

oops >> misfires ... on third loading firing pin no longer hits primer ... how humiliating in front of my friend ... a few days later my friend showed up with $150 of factory fresh Barnes full power solid copper miracle ammo ...

Whelens don't have much of a shoulder ...and the fresh annealing didn't help much.

my new Motto:

DRILL BABY DRILL .

ken

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Match Director

linoww posted this 31 May 2025

I disagree on firing pin not driving case foreword. I've tested this many times firing a case repetitive with a new primer and no load and the shoulder does get shoved back.Tested a Ruger #1,1903 and Swiss Martini 7.5 Swiss.It does eventually stop when the extractor grabs it though.

I drilled flash holes and accuracy was diminished in my experience.

I've fired 1000's of breech seat loads in my #1 30-06 this last 10 years and my lubed case works 100%.

in fact I'm.just on my last sleeve of 1000 WLP primers of the 15,000 I've gone through with this load.if it was dangerous or a "problem " I'd probably had found out by now!

"if it was easy we'd let women do it" don't tell my wife I said that!

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OU812 posted this 31 May 2025

DRILL BABY DRILL? watch your step...ha ha ha.

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Premod70 posted this 31 May 2025

It's not the firing pin in itself that drives the case forward, rather the pressures of a fired primer. The rimless case was never designed to fire at low pressures, the flash hole diameter is part of the balancing act for a safe and sure functioning firearm. Opening the hole takes away the primer forces ability to shorten the cases and induce a unsafe headspace.

Dale Flinchum

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John Carlson posted this 31 May 2025

I wrote an article for the Fouling Shot a few tears back dealing with enlarged flash holes. The goal was to stop primers from backing out, which it did. By extension it also reduced shoulder setback. Chronograph data was improved (lower es/sd) but I never have found a match director who would give me a medal for that. Accuracy was unaffected.

John Carlson. CBA Director of Military Competition.

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Idahocaster posted this 31 May 2025

Larry,

How do you go about drilling out flash holes? Do you use a hand drill, drill press, lathe? Do you remove all the brass at once or start with a smaller bit and work up in stages? Is brass work hardening a problem?

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CBA Member

Larry Gibson posted this 01 June 2025

Idahocaster

"How do you go about drilling out flash holes? Do you use a hand drill, drill press, lathe?"

I use a drill press with the cases held which is on a mill table. I have done it by hand just though. The case deprimed case is held in a padded vise and a hand drill [cord or cordless] is used. The bit is guided by the flash hole.

"Do you remove all the brass at once or start with a smaller bit and work up in stages?"

I just use the #28 drill bit and drill the hole. A sharp bit cuts a quick, smooth hole.

"Is brass work hardening a problem?"

Never found it to be a problem.

LMG

Concealment is not cover.........

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Backofthehill posted this 01 June 2025

Your mention of the power of the primer explosion reminded me of Garand's first semi-auto service rifle that powered the action by the force of primer setback. A lot of power in a tiny package.

Based on your comment on the lack of primer extrusion with small rifle primers I'm wondering if using a bushing to use small primers in a large primer cartridge would have the same effect. It's easy to drill out the primer pocket but a friend left me more small pistol primers than I'll ever use.

Thanks much!

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CBA Member

Larry Gibson posted this 01 June 2025

I've some Berdan primered cases I've converted to take SR Boxer primers. Might have to try some cat's sneeze loads in them.

LMG

Concealment is not cover.........

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Larry Gibson posted this 02 June 2025

Also should have mentioned a 9/64 drill bit works as well as a #28. Only .001 difference between them.

LMG

Concealment is not cover.........

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Backofthehill posted this 02 June 2025

Did you have to bush the primer pocket? Just tried to bush with a large rifle primer seated upside down but my SRP doesn't fit securely. Will try to seat a LRP without the anvil cup side to the pocket. Then drill and gently ream with a lathe mounted crimp remover to get a tighter fit. Doing this just as a challenge because I can. If anyone had some Freedom Arms bushings I would gladly buy a dozen or more.

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Larry Gibson posted this 02 June 2025

I use the Berdan primer to bush the pockets. Depending on the diameter of the Berdan primer they are used to convert the primer pocketed to large or small rifle primers. The "how to is in this thread;

https://castboolits.gunloads.com/showthread.php?143958-Converting-Berdan-primer-pockets-to-Boxer

LMG

Concealment is not cover.........

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shootcast posted this 03 June 2025

If you use a long Bullet so it drags / tight in lands, it should hold case even with bolt face. Fire forming the case to chamber..

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Low power loads cases shortening

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