275 Rigby .....aka 7×57.

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RBHarter
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275 Rigby .....aka 7×57.

Post by RBHarter »

First 275 Rigby sounds sexier than 7×57 .

Second a little land jam drool bait .
Virgin 1971 brass for a virgin 275 Rigby barreled 110 LH .
7664~2.jpeg
Now the drudgery ;
The Rifle was an 06' and extremely touchy about case capacity, Donna , short for Prima Donna...... 1965 Savage 110LH marked 275 Rigby on prefit Adams and Bennett 24" barrel . Currently unfired , cleaned, amateur lapped at to pick off major burrs and find tight/loose places .

New 1971 Winchester 7mm Mauser cases unfired and untouched by human hands .
3@20 total of 60 one lot .
Weigh lotted ,169.0-170.6 gr electronic scale resolves to .2 gr . Length @ 2.230 +- .002 w/Starett 2.0-3.0 micrometer .
169.0 @3
169.2 @16
169.4 @8
169.6 @8
169.8 @7
170.0 @5
170.2 @7
170.4 @7
170.6 @1
I've decided to use the largest .5 gr lot of brass and blame fliers on case variations. So cases will be 169.2 through 169.8 lots and add the 169.0 to make out 40 cases.

Cast bullets used RCBS 7mm-168 @ 178.6-179.0 gr bare , and NOE 287-150 Hunter @ 151.2-151.4 gr naked . Both gained about 1.2 gr with checks and lube applied . Sized .285 .

Bore groove dia .278×.284 . The 7-168 touches full contact about .15 on the nose the 287-150 is set off the lands about .1 as it needs to be seated to cover the lube groove.

Hornady offers data for their 154 gr SP reaching 2800 fps in a 24" barrel at 50k CUP in a Winchester M70 . Circa 1971 .

Speer offers 160 mag tip and hot core also at 50k CUP reaching 2760 in a 22" Ruger M77 . Circa 1990 .

Lyman duplicates the above even in the 50th still in CUP .

Hodgon site offers data for the same powders ......in CUP not PSI .

All sources say the cartridge should be held to 40 k CUP and starting loads . I have Sierra data also .
PO Ackley's manual only reaches 2500 fps MV using a 95' Chilean Mauser as opposed to the 29" infantry rifle or 18" carbine so likely a 24" barrel .

I mention this because because a 308 at 58 kpsi and an 06' at 55kpsi only run the high 2800s with assorted 150s in 22&24" barrels with the same powders in a larger bore and in the case of the 06 another 1/4" of case . Which would mean that the 50 kCUP is up closer to 58-60kpsi ......
I have a reference that shows CIP allowing 56kpsi and SAMMI shows 51 kpsi at only 46 k CUP . It lists a 162 gr at 2625 fps MV but doesn't list a barrel length . While I have no doubt that even the 1965 110LH will handle the Hornady, Speer , and Sierra data with CIP allowing 56kpsi and a 160 gr going 2600 fps I don't think a steady diet of 2800 fps 154&160 gr loads will do it any good .

Other oddities noted H4831 operates at higher pressure and the same velocity as IMR or H 4350 for the 175s .

All of this leaves me with a problem. I have plenty of both H and IMR 4831 and IMR 4350 which I normally would shoot at start or just below but the data suggests that they're a little squirrelly in the 7×57 . So I guess for the moment I'll consult Lyman 43 and rub some Unique on it at about 8.0 and see what happens.

After much meditation on the matter I loaded 5 ea at 8.5,9.5 , 10.5 gr Unique , and 36.0 IMR 4831 of the same vintage as the brass .
I also had 8 primed FC59 Match formed cases so I dumped 6.0 Unique in them and added an NOE 287-150 Hunter to get the scope and barrel pointed in the right general direction.
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Re: 275 Rigby .....aka 7×57.

Post by RBHarter »

I guess I didn't follow up on this .
The 287-154 delivered the best groups . The 168s weren't anything like I thought they should be velocities were as expected the barrel was clean but it grouped 3-4" at 50 yd.

Another group of fellows that seem to have a good handle on things suggested that it might be a relationship between fit and sizing giving me grief . Among other things the length of the throat might not be right or even close .

The headspace is tight enough to make nominally sized WW new brass a little bolt gritty to very firm to close .

The above is an important detail. I intended to do a setback and ream the chamber , it's a Savage and there is room for a thread or 2 and ream for HS . Which would have "the fit" . For investigations sake I grabbed a fire formed case and matched up the shoulder for shape .
The neck looks long on the reamer so I tried to measure some points . That didn't work out well .
I yanked the expander out of a sizer die and a piece of 25-06 from 06' case and made a 7×57 case that would slip the neck into the throat and leade . Pistol primer , it was out on the bench , and 8-9 gr of Unique under a case balance of Grits and a wax cap . I think I have the fit issue located. I generally do this for new to me arms and didn't for a brand new unfired barrel because,you know it's a brand new unfired barrel.
The NOS brass shortened a little filling out to 2.225-2.226 . The form and measure case gave me a neck all the way out to 2.270-2.275 . I'm thinking the neck being being.02 from the end of the chamber could be a contributing factor in the fit .
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Re: 275 Rigby .....aka 7×57.

Post by RBHarter »

A picture would go a long way here .
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