Low pressure shoulder set back?

[SavageKustoms]

I think this is the right place to post this, chastisement is welcome if not...
Been reading a lot of C.E. Harris articles in preparation for loading low velocity cast in bottleneck rifle cartridges.
The question:
Is flash hole drilling necessary to extend brass life, or facilitate proper ignition? Basically, do I have to, or should I? Am I looking for reliable ignition, or case life?
As always, any input/experience welcome.
Many thanks!

Edited for clarification:
I'm talking about very low velocity. As with the Lee 314-90swc or round ball loads. However, is this a concern with light 150-170gr projectiles as well?
Thanks again.

[Hick]

I have not done any research, but I don't think you need to drill the flash holes. Ever fired an empty case with a primer in it? The flash comes all the way out the barrel, so I think it is likely it will ignite anything in the case. Anyway, I mostly shoot low velocity, all the way to sub-sonic, using small quantities of pistol powder in 223, 30-30, 32 WS, 30-06, 7.65 Argentine, 7.62 x 39 and 303 British. Never drilled flash holes, never seen ignition problems, and have many, many cases I've reloaded up to 20 times. I only neck size and have never needed to set back the shoulders either.

[SavageKustoms]

Hick, I was of the same mind. Reading a bunch of info sort of made me question everything. If you only use the brass in one chamber, it'll fit. However, if the shoulder keeps moving, that sounds like eventual failure. That brass can only move so much, before it cracks. I was assuming ignition was not the reason, but lower initial pressure in the primer pocket. After all, it doesn't take much to seat a primer, probably less to push it out of the pocket.

[beemer]

I have had shoulder set back in my 8 X 57 mauser using light loads. Drilling out the flash hole helps. Ignition was not really a problem. I set aside 50 cases for that purpose. You didn't say what you are shooting Just give it a try before you alter any cases, your load might be fine.

Using the same load for a 308 win seemed to give less problem. The bore in the 8mm is bigger so less pressure. I have often wondered if the smaller shoulder of the 8mm makes it worse.

Supposedly the firing pin drives the case forward and the primer backs out when it fires and there is not enough pressure to move the case back. Due to the larger flash hole less pressure builds up in the primer pocket. Rimmed cases don't have this problem. What ever it is the larger flash hole helps.

[Delkal]

I would never drill out a primer flash hole to make a load work. No idea what your load is (need a lot more information) but my first thought is to use a faster powder. Or bump up the powder charge till the case seals if the load is lower than published max.

Read up on "cats sneeze" loads, IMO this is for advanced reloaders only but they can get extremely low velocity loads with just a few grains of a fast powder. Never once read that they needed to open up the flash hole.

[M-Tecs]

Various tests have shown that drilling the primer pockets doesn't affect pressure. Drilling the primer pocket does lessen the prime pushing the case forward reducing the cases actual shoulder dimension.

Drilling primer pockets is a must with wax bullets or BP blanks for horse mounted ballon competitions

[Hick]

Hick, I was of the same mind. Reading a bunch of info sort of made me question everything. If you only use the brass in one chamber, it'll fit. However, if the shoulder keeps moving, that sounds like eventual failure. That brass can only move so much, before it cracks. I was assuming ignition was not the reason, but lower initial pressure in the primer pocket. After all, it doesn't take much to seat a primer, probably less to push it out of the pocket.

Well, its a good question. Don't know what else to add other than 10-20 reloads in my guns doesn't seem to be producing a problem. But, as we all know, each gun is a law unto itself.

[SavageKustoms]

My plan is to start with 20 cases that have been fired in the chamber I intend to use. Full length size one time, and load the "light, low velocity, cat sneeze, mouse fart" whatever you want to call them, loads. Closely inspect the brass after the initial firing, and probably record some basic measurements for reference later. Modifying a single box worth of brass, if necessary, for an experiment, doesn't seem to be wasteful. Heck, if it makes the brass last longer, great. If not, lesson learned for myself and everyone here. I'm not a mathematician, but it makes perfect sense that a larger flash hole will reduce pressure within the primer pocket itself. !(Not load pressure obviously)! Bigger hole, lower restriction. I would prefer to leave the cases alone, but like I said, experimenting with a small batch, and setting them aside only for that purpose, isn't a huge deal.
Greatly appreciate the input so far. Keep it up folks!

[K43]

We need Mr. Gibson or Mr. Harris to explain drilling flash holes how and why.

[BK7saum]

We need Mr. Gibson or Mr. Harris to explain drilling flash holes how and why.

I know that there is/was a lengthy thread on this matter. Either the thread was started by Larry Gibson as a tutorial of why/how to do it or he was a major contributor of experimental information with conclusions.

[Rapier]

Accuracy comes from consistency, so in order to produce accurate loads at any velocity it is necessary to prep your brass, have consistant weight and full fill bullets, good lube, etc., otherwise just throw rocks. There is no short cut to accuracy.
If going bang is you objective, a toilet paper wad is plenty good enough. And for case forming a toilet paper wad and 5 grains of 231 will usually do the job with no bullet at all.

[Larry Gibson]

We need Mr. Gibson or Mr. Harris to explain drilling flash holes how and why.

An old post;

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 ole drilled cases for all my rimless cartridges with squib and really light loads.

Further pressure testing in the .308W the last few years indicated that loads with a psi above 12,000 will obdurate sufficiently to prevent the primer from driving the case forward thus setting the shoulder back.

[Larry Gibson]

Results of further comprehensive pressure testing as posted in these two threads demonstrates the non hazard of properly drilled out flash holes, even at top end cast and jacketed bullet pressures.

https://castboolits.gunloads.com/sho...oles-dangerous

https://castboolits.gunloads.com/sho...um-and-45-Colt

[K43]

Thank you Mr. Gibson!

[SavageKustoms]

Thank you Mr Gibson! That is exactly the information I was looking for. Appreciate you taking the time to post it.
Many thanks.

[stubshaft]

Anneal the necks. I have found that a dead soft neck helps sealing the chamber and minimize the effects of overpressure.