The UK's Finest Independent Forum for Shooters and Gun Owners. Est 2010.

Laurie wrote:It puzzles me as to how the 458 SOCOM can be made to fit the M4 / AR-15 platform as it uses a 0.473" rim diameter as per 7.92 Mauser, 308 Win, .30-06 etc. Normally that requires a larger diameter bolt than the smaller AR platform can accommodate and the 'big AR' (ie AR-10) is needed. The largest standard rim size normally used in small ARs is that of the 6.8mm SPC (0.422") and 7.62X39 / Grendel (0.447"), and the latter is known to so thin the bolt lugs out that cracking is common after a few thousands of rounds fired.

The other question I'd ask is what is extraction like in a straight-pull given the lack of gas power? Manual AR-10s in 260 / Creedmoor / 308 are a pain to work because they need so much effort to achieve primary extraction. I know the 458 SOCOM is a low-pressure round compared to them, but it still has a much larger case body to chamber walls contact area than the 223/6.8 cases.

Both the 458 SOCOM and the 450 Bushmaster round are designed for the AR-15 platform and use a .473" bolt face. I don't know how they managed it but the larger rim appears to work in the AR-15.

Yes, I know Bushmaster did it, just wonder how. I can only assume that there is a complete redesign of the bolt / bolt carrier (and the inside dimensions of the upper assembly to accommodate a larger bolt assembly too?). It suggests that unlike 223, 6.8 etc ARs, whilst the lower assembly will still be built out of a choice of standard off the shelf components, the upper needs bespoke (expensive?) bits. It'll be interesting to see if anybody with practical experience comments.

After Remington / Freedom bought Bushmaster, they introduced the Remington R15 MSR (Modern Sporting Rifle) for American deerhunters who like the black rifle in .30 Remington AR, a development of the 450 Bushmaster. It has an even larger rim diameter at 0.490". After the usual launch hoopla, there seems to be complete silence on this rifle and cartridge suggesting they haven't been a commercial success. (Not too many deerhunters, even of the small whitetail species fancy being restricted to a 125gn 0.308" bullet maybe?)

There are now a few manufacturers that do dedicated .458 AR's as the conversions/uppers apparently have a habit of cracking lower receivers. A Youtube channel called Demo Ranch uses them in a few videos

Laurie wrote:
The other question I'd ask is what is extraction like in a straight-pull given the lack of gas power? Manual AR-10s in 260 / Creedmoor / 308 are a pain to work because they need so much effort to achieve primary extraction. I know the 458 SOCOM is a low-pressure round compared to them, but it still has a much larger case body to chamber walls contact area than the 223/6.8 cases.

I'm not exaggerating when I say the extraction on my SVD (7.62x54r) is like silk, almost easy as a bolt action and and can be done with one finger.Never had extraction problems with my AKM or Simonov SKS,both in 7.62x39,either.

I know - I had a borrowed Izhevsk Tigr-0 whatever model on loan for review maybe 15 years back. Very easy operation in 7.62X54R. AR-10s in 308 and 6.5 Creedmoor, forget it. One grain above starting loads and it was a two-hand job to get the bolt to start! Must have something to do with the case taper.

Lmt .308 here. No problem with extraction.

I only use factory ammo and mostly GGG 168gr match.

Only time it got sticky was after 20 rds on a hot day. And even then, it just needed a yank rather than a pull - still no more than two fingers needed - if that makes sense !

Laurie wrote:I know - I had a borrowed Izhevsk Tigr-0 whatever model on loan for review maybe 15 years back. Very easy operation in 7.62X54R. AR-10s in 308 and 6.5 Creedmoor, forget it. One grain above starting loads and it was a two-hand job to get the bolt to start! Must have something to do with the case taper.

I tried a mates L1A1 and the extraction was awful, you really had to Yank the bolt back.He tried some MEN ammo in it and had to knock the bolt back with a lump of wood to get it to extract!

snayperskaya wrote:
Ok.....you don't know what you're missing!.

With a Finnish Mosin, we don't miss much at all. 'Speshully Russkies....

meles meles wrote:

snayperskaya wrote:
Ok.....you don't know what you're missing!.

With a Finnish Mosin, we don't miss much at all. 'Speshully Russkies....

Finnish Army also use the Dragunov.......and enlighten me on how many Russian's you have shot lately???.

snayperskaya wrote:

Laurie wrote:I know - I had a borrowed Izhevsk Tigr-0 whatever model on loan for review maybe 15 years back. Very easy operation in 7.62X54R. AR-10s in 308 and 6.5 Creedmoor, forget it. One grain above starting loads and it was a two-hand job to get the bolt to start! Must have something to do with the case taper.

I tried a mates L1A1 and the extraction was awful, you really had to Yank the bolt back.He tried some MEN ammo in it and had to knock the bolt back with a lump of wood to get it to extract!

Does that feller shoot at Minsterley? If so I saw him and his lump of wood.