M1 Garand 1:12 Match Barrel: Does Bullet Weight Really Matter?

[Mountain]

My match M1 Garand was built with a 1:12 Krieger barrel rather than the usual 1:10. Supposed to be better for lighter bullets, such as 155's rather than 168's. Honestly, I could never really see a difference given other factors spreading out my shot on paper. Took an inventory of my 30 cal match projectiles last night as saw that I had SMK 125's and TMK 175's. Time for a more definitive experiment!

Decided to use my trusty old Varget as the powder and some Lake City '67 Match brass that I had just prepped. Starting load for the 175's is 45.0 gr and for the 125's 54.0 gr. Somewhat concerned about over-gassing with the 54.0 grains but neither do I like loading below minimums unless it's a known 'light load' powder. I have a fresh Orion7 op rod spring, so it should do OK.

So which one is which? My first shots were only for groups of 5, then I shot for score with the next 5. Yeah, it would be more statistically significant if I shot more groups but this was just a quick and dirty look-see.

Target on left, the first shots at bottom left corner. Missing 3 to the left at about the same elevation. Group at center, I made two windage adjustments and the 3 closest to the 'X' are their own group, at around 1.11".

Target on right first shots at upper right and stringing vertically a bit. Shots for score spread all over the 10-ring with a windage and an elevation adjustment. Group of last 3 at center X, 9:00, and 12:00, at around 1.57" iirc.

So which was the 175 and which was the 125?

 

[johnN]

175's left. 125's right. guess based on my 150's vs 175's are like that. heavy and slower are low.

 

[Mountain]

Barrel twist isnt just about bullet weight

Bullet length factors into this as well

Longer and/or heavier bullets require a higher twist rate for stabilization.

The M1 Garand 1/10 barrel was designed to be used with 30-06 M2 Ball

If you're going to use different ammunition then all calculation/estimation should proceed from deviation from the M2 ball specs.

M2 ball specs call for IMR 4895 which is a relatively fast burning propellent for the spec of projectile length/dimentions as per below

http://pdf.textfiles.com/manuals/MILITARY/united_states_army_tm_43-0001-27 - 29_april_1994.pdf

Lighter bullet requires more charge for an appropriate propellent to achieve proper gas pressures/volume for gas system yada yada yada

This is a subject that has quite literally been beaten within an inch of its life in CMP and other similar forums where there are mounds and mounds of info people have posted

Nice reference- thanks for posting. Curious if the specs for chamber pressure are old CUP method or transducer generated. M2 Ball via the 50 gr of 4995 is generating 50,000 psi chamber pressure according to the document. My typical 155 gr load and the hotter of the two loads above are generating ~45,500 CUP. Accounting for any difference in CUP vs. psi, probably not that different. I'm assuming the military manual is listing a transducer generated psi. Anyway, I'm at Hodgdon minimum loads for .30-06.

There are mounds and mounds of info, but seems like about 80% of the mound is "What if I do this?" followed by 'You should do that." without any report of actually trying the different conditions and results. Yeah, just a few shots isn't very scientific of me, but I'll at least do it and report. I go into much more detail for longer distance shots 600 yards and beyond, but for 200 yard iron sight matches I think we don't have to do much hair splitting.

When working up loads for the M1 and M1A, I'll stay within the confines of 1. adequate energy to reliably cycle, 2. not so much that I beat the crap out of the rifle (and me), 3. enough case fill for consistent ignition, and 4. projectiles that are stable within the confines of max OAL and the rifle's particular twist. I've settled on Varget because I get good results and it's quite temperature stable as I will shoot in any weather- even below zero. After that, it's what groups well.

For further refinement I'll break out the chronograph and check SD and ES. If those values are relatively low and I'm getting good groups, I'm done. My personal limits for skill and eyesight are around 1.1 to 1.2 MOA 5-shot groups at 100 yards via iron sights, shooting off the bench or via sling and sandbags. I have loads that will do that consistently in my .308 M1 and M1A. Not quite there yet with the .30-06 M1 but getting close. Here's a 100-7X via same M1 on a Dirty Bird target for a postal match last year.

 

[mac1911]

F twist rate ....load them up them up and shoot them out...... Heck the 1/10 twist is a hold over from the long 173 grain M1 ball bullets.

I will say this for the most part until you start using some really long for weight bullets....those 155s and even the 168s are pretty short and fat really.

175s on the left!

quick load puts your 125s at around 48k psi and touch over 3000fps ....many say the 125s really like that 2700-2900fps range ?

the 175s come in a tad lower on chamber pressure but both are right around 10k psi at the gas port.
175s are 2440fps per Quick Load

have fun

If you run the one of the twist calculators for the 175s your still to fast at 1/12 ? Run bergers calculator 1/12 is fine.

See Mountain you missed the cool kid twist of 11.5"

 

[Mountain]

175's left. 125's right. guess based on my 150's vs 175's are like that. heavy and slower are low.

F twist rate ....load them up them up and shoot them out...... Heck the 1/10 twist is a hold over from the long 173 grain M1 ball bullets.

I will say this for the most part until you start using some really long for weight bullets....those 155s and even the 168s are pretty short and fat really.

175s on the left!

quick load puts your 125s at around 48k psi and touch over 3000fps ....many say the 125s really like that 2700-2900fps range ?

the 175s come in a tad lower on chamber pressure but both are right around 10k psi at the gas port.
175s are 2440fps per Quick Load

have fun

Surprisingly, the 175's were not on the left. Doesn't make sense, but here's what happened:

Rifle was still sighted for last month's CMP match, where I shot 155's if I recall correctly. I figured the 175's would drop lower, and worst case if they were equal they should hit center of the blue 'ghost' rings. Oddly, they hit slightly right and way high. Made an adjustment to try and hit center and then a couple more clicks before last 3 shots near center.

I didn't change the sights and switched to the 125's. I figured they would be close to center and probably way high vs. the 175's. Wrong, way left and way low. Probably the windage and elevation I had for the 155's would have been about right.

At least the 125's are going to potentially group as well or better than what I've been able to do with the 155's. I have other rifles that can use the 175's.

 

[mac1911]

I have not shot a lot of SMK 175s but so far all loads have done well. 125s can be like lazers at 200 yards. SMK's are just a tad to expensive for my needs , rifles , skills. Im not going to see a huge gain spending close to double on SMKs vs Noslers
They are short and fat for thier size.
If nosler has those 130 gn on sale anytime soon i will be snagging more. They do very well in the K31.

 

[mac1911]

Barrel twist isnt just about bullet weight

Bullet length factors into this as well

Longer and/or heavier bullets require a higher twist rate for stabilization.

The M1 Garand 1/10 barrel was designed to be used with 30-06 M2 Ball

If you're going to use different ammunition then all calculation/estimation should proceed from deviation from the M2 ball specs.

M2 ball specs call for IMR 4895 which is a relatively fast burning propellent for the spec of projectile length/dimentions as per below

http://pdf.textfiles.com/manuals/MILITARY/united_states_army_tm_43-0001-27 - 29_april_1994.pdf

Lighter bullet requires more charge for an appropriate propellent to achieve proper gas pressures/volume for gas system yada yada yada

This is a subject that has quite literally been beaten within an inch of its life in CMP and other similar forums where there are mounds and mounds of info people have posted

I have been looking for a newer small arms tech sheet. Seems 1994 is the only one out there. Figure with all the advancements in powder additives IMR4895 would not be the best choice......then again .gov/mil is not always out for the best Good Inuff is usually sufficient.

 

[Mountain]

IIRC, the TMK 175's were on sale cheap- like Nosler overrun cheap. Bought a bunch and must have tried a few then forgot about them. Maybe not a popular size.

As far as price goes, I try not to buy SMK / TMK's without some sort of sale or online coupon, and I don't shoot them all the time. I have a bunch of those cheap Match Monsters but so far not happy with the accuracy with mild loads. I'm going to try them loaded a little hotter and see if I can squeeze in the groups a little.

Can't for the life of me explain why the 175's were hitting much higher, was expecting lower at the same elevation used for 155's.

 

[mac1911]

IIRC, the TMK 175's were on sale cheap- like Nosler overrun cheap. Bought a bunch and must have tried a few then forgot about them. Maybe not a popular size.

As far as price goes, I try not to buy SMK / TMK's without some sort of sale or online coupon, and I don't shoot them all the time. I have a bunch of those cheap Match Monsters but so far not happy with the accuracy with mild loads. I'm going to try them loaded a little hotter and see if I can squeeze in the groups a little.
Can't for the life of me explain why the 175's were hitting much higher, was expecting lower at the same elevation used for 155's.

Heavy bullets hang onto velocity better . So depending on your velocity of the 155vs 175s ....well you need to run it through a ballistic calculator. Or better yet post the question on "PMS" forum and watch the fun.
Im not sure but the TMK where not welcomed with open arms when they came out? I also think they might have been suffering the same fate as Hornady with tips melting?

 

[Mountain]

Heavy bullets hang onto velocity better . So depending on your velocity of the 155vs 175s ....well you need to run it through a ballistic calculator. Or better yet post the question on "PMS" forum and watch the fun.
Im not sure but the TMK where not welcomed with open arms when they came out? I also think they might have been suffering the same fate as Hornady with tips melting?

LOL, great idea- let the grumps on the PMS forum chew on it for a while. There will be one or two with excellent, experience driven answers and others who just want to argue their opinions.

Hadn't heard about the tips melting. I've shot the Hornady's in my 6.5 man-bun out to 400 yards with no issues. Maybe someone shooting one of those 4,000 fps RUM's or something?

Tips melting reminds me of a side story about the sabot projectiles for the M1 Abrams tank. During the first Gulf War I was working with a defense contractor to improve the accuracy of these things. The 'dart' had a steel shell filled with spent uranium and some fins made from anodized aluminum. The trick was to get the finishing and edge radii perfectly uniform. The aluminum melted inflight from the air friction, so the surfaces had to be extremely uniform so it all started melting at the same time. If one or more fins started melting early, no bueno. Don't think that is classified info- if it is, I'll write from club fed.