Mexican reloads but with varying bullet weights.

P

Pond James Pond

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There is a practice of taking a given complete cartridge (usually milsurp), pulling the bullet and replacing it with another, better bullet of the same weight and profile. The method, I believe, is affectionately called "Mexican Reloading".

I have done this with 150gn SPBT instead of 147gn FMJBT. It worked fine.

So here the difference in bullet weight was a mere 3gn, but I started thinking:

What if I had a 168gn bullet I wanted to use. Needless to say a straight swap would be ill-advised, but what if I did it incrementally: used the original 147gn bullet's charge as max charge basis for a "10% off" ladder under a 150gn bullet.

Let's say that I was then able to establish charge weights that worked fine and I then took the median charge weight and used that as the next starting point for another "10% off" ladder, but this time under a 155gn bullet.

Then I could repeat the same "10% off" the "median as max" from that latest ladder to find good charges for a 160gn bullet, repeating the process in as incremental a fashion as I can until I find a charge weight range for my putative 168gn bullet.

I don't know if that makes sense, but assuming it does, would this seem a relatively low risk way of finding the powder charge for an unknown powder in a regular cartridge?

(not planning on trying it, but curious if my logic meets with peer approval from those who may even have tried it...)
 
The term you are looking for is "Mexican Match". US military shooting teams would pull the old M118 173 GR match bullet and replace it with a 168gr or 180gr Sierra Matchking.

There have been a couple threads on it in the past, but in my view once you start messing with the powder charge, it becomes more trouble than it is worth.

In theory, you could dump the powder out of a few rounds and take the average, to determine the charge weight, but the problem is that it would only work for that lot of powder, and you have no way on knowing when lots changed. Government arsenals and ammo manufacturers don't use canister grade powder, they buy large lots of bulk powder which does not have the same consistent burn rate of the commercially available stuff.

Powder companies sell canister grade to consumers because the jug of 4064 you buy today needs to burn exactly the same as the jug you bought in 1990 (or 1970 for that matter). Ammo manufacturers do not require the same level of consistency, they adjust the powder with each lot to meet their required velocity/pressure needs.
 
In theory, you could dump the powder out of a few rounds and take the average, to determine the charge weight, but the problem is that it would only work for that lot of powder, and you have no way on knowing when lots changed.
Click to expand...

I've already done an average check and the powder has been the same (printed on the box they come in).

The lot may be different, but then surely the same can be said of powders that we buy. I find a charge weight with lot X of powder B. Am I supposed to then redo a charge ladder the next time I buy powder B, in case it is no longer lot X?
 
Max load pressures between a 150 and 168 using IMR4064 are very very close. 57,100 PSI vs 58,800 PSI respectively. However, milsurp ammo doesn't use IMR4064.
7.62NATO Match ammo is a 173 grain bullet at 2550 fps using IMR4895, Stateside. Might not be IMR4895 where you are. Max NATO pressures are 60,191 PSI for Ball.
JUST swapping a 150 for a 168 and NOT mucking with the powder at all will likely be fine. No 'ladders' involved. Trying it certainly will not blow anything up.
Don't really think it's worth the effort though. Takes less time to work up a load using a 168.
 
The lot may be different, but then surely the same can be said of powders that we buy. I find a charge weight with lot X of powder B. Am I supposed to then redo a charge ladder the next time I buy powder B, in case it is no longer lot X?
Click to expand...

No, because the canister grade powders you can buy are made to be extremely consistent from lot to lot. For some reason I think it is ±3% of burn rate, but my memory may be off a bit.

Bulk-grade powders ammo manufacturers buy are not held to the same requirements, the manufacturers will tailor their load for a particular lot of powder (which could be tons of powder) to their specifications using tools that normal reloaders do not have, like pressure test barrels.

Back when surplus powders were available, it was common to find the jugs marked with "Fast Lot" or "Slow Lot" depending on how that specific lot of powder compared to the canister grade equivalent. They often had notes to use a completely different powder for load data because of this.

Powder you buy and powder ammo manufacturers use are not the same thing.
 
"The lot may be different, but then surely the same can be said of powders that we buy."

That is incorrect. Canister powders are held to a specific standard. Factory loaded and/or military ammo is loaded to a specific performance level regardless of the powder used.
 
James,

Read this before assuming bullet weight alone is a safe criteria.

I used QuickLOAD for a quick look at several powders to see what happens when a charge that is maximum with a 147 grain Sellier & Bellot 7.62 Ball FMJ bullet instead gets a 168 grain SMK bullet. Pressures increased between 16% and 20%, depending on the powder. A 10% charge reduction is will actually bring pressure down more than that with most rifle powders, but I think its a good number to start from with them, since I don't know what you have. The 168 grain match bullets, in particular, tend to have thin jackets, so I don't think bullet hardness difference, as mentioned in that article, will cause you a problem going in the 168 grain match bullet direction.
 
Mexican Match

What a racist , insulting thread! Shame on you!

Should be called something like South-of-the-Border Match Maker.

What do you think?? :confused:
 
Yeah, they were clearly racist holding the 1959 Pan-American Games in Mexico City, where the term originated.

Sometimes I roll my eyes so hard it is actually painful.
 
I did a ton of Mexican Match stuff when I was running the AK NG Marksmanship unit.

Most was Pulling 173s from M118 and replacing with 168 SMKs for Across the Course Matches (200, 300, & 600 yards) or replacing the 173s with 180 SMKs for 1000 yard matches.

Note: The 180s of the 70-80s isn't the same as todays 80 SMKs, it closer to the 175s.

We stopped the Mexican Match when the M852 Match ammo came out, which was basically the same as our MM, that being the 168s.

At the time equipment was wearing out and M118 started being called SB (special Ball), and the quality really went south. We used the M852 for Across the Course and hand loaded for the 1000 yard ammo used in our M14s for 1000 yards.

I retired in '92 so that was a while ago.

Recently I tried some MM again, Using the CMP Greek M2, pulling the bullet and inserting 155 pulma bullets. This ammo was used in CMP GSM matches fired at the SR (200 yard NRA) targets. The X-10 ring of this target is 3.5 MOA. In short, it wasn't worth the effort. My rifles (Garands, M1903a3, M1917s are more then capable of cleaning the targets with the Greek surplus. Not worth the effort or expense. Money and time would be better spent getting ME to the point where I could shoot as good as these Rifles.

Again that's 200 yards, when I move out to 300 - 600 yards for the Vintage Sniper matches I reload.

I have ton of Greek Surplus brass and it works quite well for reloading 168 A-Max or 168 SMKs.

But there is a problem. The Greek surplus has a big difference in brass weight from year to year, and it comes mixed with several years.

I tried sorting the ammo by year and found it too was a waste of time. Looking at the 200 yard target I couldn't tell the difference between lots, I found mixed lots shoot the same as sorting. This shouldn't be the case but it is.

Why, I started measuring the powder in the cases and found out it too varies. It varies corresponding to the weight of cases. Arsenals don't get hung up on consistency through the years, but adjust their components to get consistent results. The Army has no plans on reloading their ammo.

What I'm saying, is you cant expect change one or more components and come up with a standard result.

The Quick Load Program was mentioned. Its an excellent program that you can put in changes of components and see what happens with out the danger of destroying your firearm. If you get high pressures in Quick load, change something until you get the desired pressure. Its a pricy program but its well worth the price if you do any reloading at all.

I've found it to be an excellent program as the resulting velocities come pretty close to the results I get over the coronagraph.

But Quick Load wont tell you what the accuracy result will be. Only your rifle and target will do that. And if you remember that velocity doesn't mean accuracy PLUS pressure may.

I really don't see any reason to Mexican Match ammo today, but if I would I wouldn't mess with the powder. The powder is matched to the case and not so much the bullet. You start messing with the powder, without taking case weight into account you're wasting your time and could cause problems. Not many of use have the pressure gages and equipment to check pressure.

One would be better served by just reloading to match your rifle and accuracy you desire for your given task.

Regardless of what you do, the weakest link will always be the shooter, and for best results, that is the part we should be working on.
 
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