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257 Roberts Improved...fire-forming...Powder...Fast or slow ?

dolek

dolek

I am looking for opinions from those that have fire-formed 257 AI . I have researched this and see folks on both sides so I thought I would ask for some real world info . I can't catch any shoulder so I am jamming to hold tight to the bolt face . I had read that Mr. Ackley used slow powder for fire-forming. I used a mild load of H 4831 on my first try . This is a new one to me and I played it safe . I only have brass from Hornady +P fired in this rifle for a base . Compared to that my fire-formed brass looks like it is about 90% formed .

Should I be aiming for blowing things out on first firing or is two OK in the 257 AI ?

Thanks
 
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Preacher said:
I prefer to run my fire forming loads on the hot side with a little faster powder than I'll end up using..
Really want them formed the 1st time out..
Click to expand...
Thank you,my gut was telling me just what you say . I had my doubts about slow powder and light charges .
 
I have had several in this caliber, and I think one was headspaced longer than it should have been. I had to seat the bullets way out to jam the lands...then the parent case would fire form. It might take 2 firings...
the others did fine with regular .257 +P ammo. Accuracy was acceptable (to me) the second rifle would fire form the first time...
 
I had a .257 AI for years and now I have a 6mm AI. In an ideal world the AI chamber will be short to enable a crush fit and with enough pressure cases will be perfectly fireformed either with cream of wheat (COW) or bullets. But with excessive head-space case stretching and potential case separation will occur. Another solution to the problem would be to neck up brass then neck down to create a false shoulder to enable a crush fit then COW fireforming; I don't need to do this with my 6mm AI - nice crush fit with unformed brass. I do make .280 Rem cases from .270 Win with a false shoulder - up to .30 than down to .28 with the new false shoulder to give a crush fit with COW- have lots of PPU .270 brass.

Should I need to fireform with bullets I would select a matching pressure factory load using some powder that filled to case to at least 85 percent. I have heard that some light loads using slow burning powder have caused some detonation effect.
 
Thanks guys, I can't get a crush fit so I seated long . I tried H4895 ,started at a safe spot and worked my way up to where the brass looked like the factory +P stuff . I am very close but not fully blown out yet ,second firing should do the trick .

I will see how this batch performs as far as longevity, etc. . If I run into short life I will have to go the false shoulder method .

When fire forming are you guys up in the AI powder charge range or forming within the straight up 257 Roberts range ?

Your help is much appreciated.
 
I also did the cream of wheat method with my 6 AI. I used winchester231 powder. 12 grains and stuffed the case neck with bit of cotton ball and used a quarter of a square of toilet paper to act as the wad/ separation between the powder and C.O.W.
 
I used Hornady brass to fireform my 250/3000AI and had to resort to annealing to get them to form. Otherwise I was looking at 2 or 3 firings to get formed with max 250/3000 loads. I think that was with IMR 3031. I even went higher but got pressure signs so resigned myself to annealing. I would feel alot better necking those up and then back down to get a crush fit at the neck rather than relying on bullet jam.
 
I am forming my first batch of 257 improved brass also. I am having good success with a warm load of RL15 and sierra 87s.
 
long40shot said:
I am forming my first batch of 257 improved brass also. I am having good success with a warm load of RL15 and sierra 87s.
Click to expand...
Excellent,glad it's working well . Are you able to get a "crush" fit ? What brand brass are you forming,if you do not mind sharing .
 
Evan said:
Can you take it to your gunsmith and have him set the headspace tighter? Take a couple pieces of brass for him to use. I've never had much luck fireforming with only bullets jammed. Tight fitting brass always forms better.
Click to expand...
It is an option if need be . When you say you did not have much luck was it due to brass failure or were you not happy with the way it turned out ? Thanks
 
daleboy said:
It is an option if need be . When you say you did not have much luck was it due to brass failure or were you not happy with the way it turned out ? Thanks
Click to expand...

I got several failures to fire, light strikes, and it took 3 or more firings to get them formed. At the time, I wasn't wise enough to know to check for brass stretch in the body walls with a paperclip or similar. I might have found that I had thin spots if I had. Far as I recall, my starting brass was 0.007" shorter headspace than the chamber.
 
Evan said:
I got several failures to fire, light strikes, and it took 3 or more firings to get them formed. At the time, I wasn't wise enough to know to check for brass stretch in the body walls with a paperclip or similar. I might have found that I had thin spots if I had. Far as I recall, my starting brass was 0.007" shorter headspace than the chamber.
Click to expand...
Thanks for the info,I will soon find out how close mine are after get a second firing on them.
 
I have quite a few Ackley improved calibers, including .257 AI. I use a max. load for the parent case (such as .257 Roberts) as listed in manuals. Too much pressure to load what you would use in the Ackleyized case after fire forming.
 
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Here is a pic .I was increasing powder by .2 grain going from left to right . I was using H4831 for this batch . My next batch was a hot load of H4895 ,they formed better(no pic yet) .I had one split the shoulder,the rest look OK but I fear I may have gone a little too hot .

Pic of the H4831 batch.

257 AI.JPG
 
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