minimum charge for 7.5x55

[Battis]

I've been searching and reading for info on a starting point for the 7.5x55 using H4895 with a 150 gr FMJ bullet. I even called Hodgon but they're closed.
I know not to exceed the maximum listed powder charge, but what happens if you start too low (from a safety point)?
The listed minimum charge for this round is 38 grs, though I've seen some "youth" loads at 30 grs.
I loaded a few rounds with 34 grs and they fired well, but...
How low can you go?

I found this old posting on another forum:
"But there's a safety issue with reduced loads. When the .308 Win. case gets driven forward by the firing pin, the shoulder sets back a few thousandths, the case head is now forward the same amount, then pressure rises pushing the case body against the chamber wall. The first point to contact the chamber wall is the shoulder as it's got the thinnest brass. Then contact starts moving back towards the case head stretching the case as the brass behind the shoulder is pressed hard against the chamber. Meanwhile, the primer starts to back out from pressure getting to it, too.

If there's not enough peak pressure to push the case head against the bolt face and seat the primer back flush with the case head, the fired case will have less head clearance than it did before. And the primer will be seen sticking out a ways.

I've seen primers stuck out of .308 Win. case heads 10/thousandths of an inch when normal max loads are reduced by 10 to 12 percent. I suggest one start cutting normal max loads 1 grain, shooting that round, noting if the primer's still flush with the case head, then drop another grain and shoot again. As soon as the primer's seen protruding past the case head, mash that case between your teeth to destroy it, then consider your minimum safe reduced load is 2 grains more than one that had the protruding primer."

[462]

Don't reduce a load below what your reloading manual calls for. It should tell you why, as well.

Search secondary explosive effect, if you are not using a manual.

[ShooterAZ]

This is only a problem using the so called "mouse sneeze" loads, ie: very light charges of fast burning pistol/shotgun powders. Light loads of 4895 won't cause this. If you want even further reduced loads using cast boolits, try 10gr of Unique, or 16gr 2400. Even these will not set the shoulder back.

[uscra112]

The problem with light loads in rimless bottleneck cases is that the primer explosion not the firing pin, drives the case forward, setting the shoulder back, and the subsequent pressure from the main discharge does not drive the case back again. The extracted case now has excessive headspace, and it's risky to use it again with full loads. The "fix" is to use pistol primers, which are not as energetic. Or just not shoot cat-sneeze loads in rimless cases. Those archaic rimmed cases has a big advantage there. By cat-sneeze loads, we're talking 6 or 8 grains of a pistol powder like Unique, or my favorite Red Dot in your K31. Pressures well under 15,000 psi, which are perfectly OK for pistol primers.

Quickload suggests that 34 grains of H4895 gives 20,000 psi with a 160 grain boolit, at 2000 fps velocity. I'd quit there and go to the faster powders if I wanted less velocity. H4895 will not burn consistently below that pressure. You'll get larger velocity variance, and poor accuracy. At some point it won't burn much at all, and the bullet will not exit the bore.

SEE is not an issue with 4895. This has been discussed to death on the forum. SEE results from middling loads of slower powders, and jacketed bullets with a long bearing area. Magnum primers may play a role as well. This info comes from the only actual pressure tests which were able to reproduce SEE. The jacketed bullet is driven into the throat by the primer pressure and stops before the main charge builds enough pressure to keep it going. The bullet is now a bore obstruction.

[462]

uscra112,

If H4895 isn't slow enough to produce a possible S. E. E., I stand corrected.

Battis,

For what it's worth, my K-31 and Unique are very close friends.

[Battis]

It all makes sense. If the manual lists 38 grs as a minimum, I'll start there. I have to get out of the black powder way of thinking.
I actually bought a reloading book...Reloading for Beginners or something like that. When I read the part that said "seat the bullet in the loaded case...pointy end up" I realized I had bought too basic a book. It burned well.

[Battis]

I just spoke with a tech at Hodgdons and asked how low a load can I use in the 7.5x55, with the 150 gr FMJ and H4895. He said the 60% rule applies to that powder in that cartridge (reduce the max load by 60%). The max load for that bullet is 42 grs, so he said I can use 25.2 grs. I'll probably stick with the 34 grs.

http://hodgdon.com/PDF/H4895%20Reduced%20Rifle%20Loads.pdf

[jonk]

I've gone down to 25 grains but needed a dacron filler for reliable and consistant burning, in the 7.65 Mauser which is a close relative in terms of case size and capacity. Personally I have never gotten top notch accuracy out of that powder in my Swiss guns but that of course depends on the rifle in question.

I usually run 36 gr of WC 846 (similar to BLC 2) which is a very mild load. Grain for grain this powder is similar in burn rate to 4895 so I think that 34 would probably do you well.

[madsenshooter]

The OP was wanting info for jacketed. I note he didn't say which Swiss rifle he has, that could make a difference, as they have different throats. I think SEE can be a possibility with 4895 in a long throated rifle, with things going as described above. Bob S recently tried a much reduced jacketed load of it in a 6mm Lee Navy, one with a long and rough throat. I wouldn't call it an SEE, but it sure gave him more pressure than what he wanted. Anyway OP, stay within Hodgdon's guidlines and if something goes wrong you'll have someone to blame!

[felix]

If it quacks and/or burps like a duck, let's call it a duck. ... felix

[Battis]

It's a 96/11. I misquoted the Hodgdons 60% rule - I said reduce it BY 60% of max load when I meant to say TO 60% of max load.
I shot a handful of FMJ 165 gr rounds last week loaded with 34 gr H4895. They were as accurate as I needed at 100 yds (metal gong). I also shot a few 150gr cast bullets with the same load and they were all over the place.
I just loaded up 20 rds -10 with 34 grs, 10 with 38 grs H4895 (150 gr FMJ). As soon as I dig out of the blizzard, I'll compare the two different rounds.

[madsenshooter]

Throat's a little longer than a K31's but the Swiss rifles don't generally have a rough throat or bore to worry about. Here's a link to the 6mm Lee experience I mentioned. http://www.jouster.com/forums/showthread.php?42081-Wallhanger-.....-%28

[Battis]

Interesting. Any ideas of what might have caused that? Powder, bullet, primer, brass...?

[madsenshooter]

My guess is a combination of long, rough throat, much smaller than standard charge, but within Hodgdon's guidelines, and a relatively thick jacketed bullet that has some jump before contacting the rifling of the throat. Just so happens I've sectioned a Winchester 100gr Powerpoint in the past. For a 6mm bullet it has a pretty thick jacket, certainly not a varmint bullet.