Home Forums Hunting & Shooting Ask The Gunwriters squib loads and enlarging flash holes

Hi all,

I have seen multiple references to enlarging flash-holes to prevent shoulder set-back when firing squib/gallery loads. I was just wondering if someone could explain the concept/theory behind this and why it works.

Many thanks,
Frosty

Never done it, never heard of it, and it sounds like utter nonsense.

Not exactly what you consider gallery/squib loads.

I've done the following w/o shoulder "setback" issues:

.35 Whelen @ 1,300 - 1,500 fps with jacketed pistol bullets
.30-06 @ 1,600 - 1,700 fps with jacketed bullets
.30-06 @ 1,000 -1,200 fps with cast pistol bullets
.375-388 @ 1,100 - 1,150 fps with cast bullets

Shoulder setback is what you do with a FL sizing die.

Depending on what cartridge you are working with. The shoulder setback is a misnomer for what happens with a grossly under powered load, that smokes the shoulder because it doesn't have the pressure to expand the neck which would have sealed the chamber.

This subject has been studied at length (lots on this at cast boolits website) and the jury is still out. My personal opinion is, in your usage, you experience shoulder setback then you need to drill your flash hole. Nine times out of ten, mouse fart loads will not cause any problems so....I wouldn't do it unless you clearly need to. A symptom of the problem is the spent primer backing out of the fired case. Extreme subsonic loads have many issues beside shoulder setback. Unless you use the proper powders, Red Dot, Unique, Bullseye, etc. you take the risk of a S.E.E. event at the worst..and more commonly the projectile stuck in the bore. When in doubt go with CE Harris' "universal cast bullet loads".
There is a reason cast bullet people love rimmed cartridges.

Humm and I thought I obsessed over minutia. I do uniform flash holes but it is mostly a feel good endeavor.

Well, it's not really minutiae if you get the exact pressure conditions to cause the primer to act as a tiny piston against the boltface...shoving the case ahead with sufficient force to slightly crush the shoulder. It happens occasionally. 'Mouse fart' and the more powerful 'cat sneeze' loads are susceptible and it doesn't hurt to at least be aware that it can happen. Cast bullets never hurt a shooter or his rifle...ignorance is what rings and bulges barrels on grampaws old single shot.

Have enlarged flash holes in revolver gallery loads to avoid primer set back locking up the cylinder. I avoid potential issues with bottle neck rifle cartridges by reserving cases for gallery loads only. (I Dremel a notch on the case head so there's no mistake.)

So does enlarging the flash hole help reduce shoulder set back, or does it merely prevent primer set back?

I am using fast pistol powders under HBWCs in a 35 Rem, which doesn't have a lot of shoulder to begin with. I have filed grooves across each case head so that these cases don't get mixed-up with any others.

Shoulder set back and primer set back are really the same thing; one is just an indication of the other. There is only so much room in the chamber; for the primer to back out of the case, it had to shove the case forward and set the shoulder back in doing so. If you see a case with a primer backed out, that case has the shoulder pushed back.

If you measure base to shoulder dimensions (with the primer knocked out) this becomes obvious, and after measuring a bunch of them you can even learn to estimate how much the shoulders are set back based on appearance of the primer sticking out. 35 Rem is worse for this than most, but it can happen in any cartridge. I've got a bunch of 35 Rem brass for example with the shoulders set back ~.015"-.020" from multiple uses of subsonic/suppressed loads. BTW leaving the cases lubed when you fire mild loads only makes this worse; the chamber is basically a sizing die and any force pushing the case into it can push the shoulder back.

One thing I have experimented with - and this is a bit off the deep end, but it works - is filling the cases mostly full of lead to reduce the case capacity. Small cases generate higher and earlier peak pressure with the same load, which can prevent this issue and also reduces the amount of powder needed. I did this by making a tapered plug that fits the case mouth and tapers down to fit in the flash hole at the bottom; submerging the case in molten lead and then inserting this plug produces the desired result. Of course those cases are only good for those light loads after that, but they are reloadable. If making such a plug, take into account your sizing die's decapper dimensions to make sure it still fits.

I guess I have never used loads reduced this much. Would a filler help or is it overall pressure or lack of.?

Unless you go to black powder you want enough pressure to build to get the powder to burn cleanly, but with a minimum volume of gas. Why you choose a powder with a high pressure exponent (fast burn rate).

P. T. Kekkonen wrote some interesting (fascinated me) on subsonic and gallery or "cat sneeze" loads. You can find it hereGunwriters on the Web Read on through part 2.

But be careful if you try this at home. Improperly done very reduced loads have blown up pressure barrels!

Hoo boy, fillers,,,, was there ever a more controversial subject? The original OP question, do you need to open up flasholes? Well yes, when you are at that exact balance point of pressure when the primer will back out of it's pocket but there is not enough pressure to seal the case neck against the chamber wall. Now to fillers. The most experienced and knowledgeable shooters prefer to call them "powder positioners" as that term exactly describes what the material used does...it keeps the powder back on top of the flash hole, theoretically exposing the entire reduced charge to the primer flame. Not using a powder positioner, the powder can orient itself anywhere in the case, usually wherever gravity takes it, and you will see some pretty dramatic velocity changes on the old chrono, powder up against the primer, powder down against the bullet base, laying flat etc. And that's ok, IF you use a powder that is not position sensitive, such as Unique (designed just for reduced loads in large cases) or Bullseye, or Red Dot etc etc. Using the .45-70 as an example, 4198 range of powders frequently gives finest accuracy, but, often fills less than half the case volume, a recipe for disaster...so we position the half charge against the primer with the powder positioner of choice. Now we have reliable uniform ignition, consistent velocity strings. So Mr Tejano, I honestly do not know if a "filler" raises pressure, I suspect that the popular Cream o' Wheat does, it's pretty heavy for volume. Which is why I don't use it, most people do, my preference is a little tuft of dacron. Thousands of rounds downrange in .45-70 and .44-77 with no drama. I hate drama. Especially in 150 year old heirloom rifles.

As far as powder position goes, it can be a rather inconsistent thing. Affects accuracy enough to be a problem, even with powders known to not be so position sensitive if you load light enough. With reduced revolver loads I simply raise the muzzle to the sky so the powder falls to the bottom of the case about the same place every time. With the 8x57 gallery loads with buckshot this is inconvenient so I insert a bit of toilet paper over the powder. Helps, but reduced to minimum, just enough to get it out the barrel, accuracy isn't so great anyway.

Fillers can definitely be used to raise pressure; by occupying some of the case capacity they can make the remaining capacity mimic a smaller cartridge. The lead-filled cases I mentioned above are an example, reducing the capacity of those 35 Remington cases down to somewhere approximately between the 9mm Luger and 38 Spl. cartridges.

In that example as well, the lead filler holds the powder in a central column (really a cone shape) with only a small amount of it exposed to the flash hole and the majority near the bullet itself. This works fine; in my observation it's consistent position of the powder that matters more than where in the case it is.

I've experimented with unfilled 30/06 and 35 Whelen cases with light cast bullet gallery loads - as long as the powder was positioned the same way every time, regardless if it was forward or back, velocity results were consistent and accuracy was reasonably good. However there was a significant difference between powder forward and powder back, velocity was lower with powder forward against the bullet and required a slightly heavier powder charge to meet the 900-1,000 fps target I was after.

Even factory ammo in some cartridges can produce erratic "reduced load" results.

Mike Venturino warned me years ago about a major brand of .32-20s: When he tipped his revolver (as I recall a Colt single-action) up then leveled it before firing, the ammo shot well--and primers did NOT back out.

But when he tipped the gun down before bringing it up to level and firing, primers backed out, accuracy sucked--and soon a bullet stuck in the forcing cone.

There's a wide enough variety of powders these days (along with old reliables such as Red Dot) that it's pretty easy to find one that won't require a larger flash-hole or fillers, even in such cartridges as the .22 Hornet with cast bullets at .22 LR velocities, or the .416 Remington with 210s at .41 Magnum velocities.

I've had the same experience with Titegroup (in a .44 Mag. ) in near absolute minimum loads though I didn't go low enough to start getting cast bullets stuck (not with that particular powder anyway ). The position sensitivity diminished rapidly as one approached minimum practical charges.

With that other powder (not saying in public) I ended up with 240 grain slugs penetrating only one side of a cardboard box at maybe 5 yards. Then asked myself. "Why?" Answer came back,"Just because."

I just had this happen today with reduced loads in the 9.3x62 with Trailboss and a cast 286gr bullet at about 1350fps. Two rounds out of seven failed to fire, and showed pretty light firing pin strikes. The cases have been used with these loads for 3-5 firings. How can I fix this? Should I switch to unique or one of the dot powders? Are these cases garbage, or can they be resurrected?

I only know of two ways to get these cases back in spec. Anneal and neck expand up to a larger size and then neck them back down to create a shoulder in the right spot, or jam a bullet into the rifling to hold the case head against the bolt face. Load should have enough pressure to move the shoulder forward, but not so much pressure to be unsafe.

Something I like to think about that your comment brings up: do the primers not back out at all, or do they back out and then get pushed back in again when the case head sets back against the breech face under pressure?

The evidence suggests to me that if there is clearance, the primers pretty much always back out but get pushed back in with higher pressure loads. That's pretty hard to prove for certain though.

One bit of evidence for this I've seen is very flattened primers with normal loads. With the same load, changing only the case head clearance has resulted in flatter primers with more clearance - one reason why primer appearance is a poor indicator of peak pressure. What I think happens here is with enough clearance, the primer backs out under it's own ignition force (remember the primer is an explosive that burns much faster than the case can build peak pressure), maybe starts to bulge slightly, and then the case head is pushed back to the breech face which irons that bulge out down to the face of the primer.

What I haven't come up with a reason for is why any primer wouldn't back out, if it has clearance to do so? (except when large flash holes are used)

Please excuse my ignorance but what is occurring with a larger flash hole? I could see it improving ignition but it also seems like it would allow more pressure to back out the primer. Again I have not gone to really reduced loads never lower than plinking, youth or reduced recoil hunting loads.