My problems sighting in modified Mauser M48...

[AlexI]

Hello guys,

I need some help here, to make sense of the problems I am having with my rifle.

First of all, the rifle itself: I got a Yugo M48 (8mm Mauser), dropped it into that pseudo-Scout ATI stock (http://www.atigunstocks.com/product-mauser98stock.html), installed a Timney Sportsman trigger (set at about 2 - 2.5 lbs pull), installed a forward mounted scope (first cheap NCStar 2.5x pistol scope, just replaced with Burris 2.75x scout). Also, I recently cut the barrel down just behind the front site base and re-crowned it (my first attempt at this, using hand tools and a brass lap with abrasive to break the edge of the flat crown). BTW, my amateur chop job didn't seem to make anything worse, the groups (first groups of the day at least) actually looked a little better after it.
Ammo is the cheap Turkish surplus stuff.
I am shooting off Harris bipod, from the bench (for sighting in, at least).

Based on what I read, I hoped for solid 2MOA performance from this combination. Sounds realistic, right?
Now, what I think happens (after several confused shooting sessions trying to sight it in and keep it there) is that accuracy deteriorates very quickly with shots fired through the rifle after the last cleaning, and letting it cool down doesn't seem to help much.
Starting with cold and clean barrel, I can usually get fairly good groups for the first 10 shots or so (maybe a little more, with longer intervals between shots). I have gotten a couple 3 shot groups in a row of 1.5" - 2" at 100 yards, and 3" - 4" at 200. But then, as I continue shooting groups and making adjustments, accuracy starts quickly going down the toilet. By about 30 shots, groups grow to 5 - 6 MOA and even the group center shifts randomly by several MOA... I tried letting the barrel cool down until it is just warm to the touch, but it doesn't help much. On the other hand, the breach part of the barrel is all enclosed with plastic in this stock, so may stay hotter a little longer?

So, does it make any sense that the barrel is just getting dirty that fast and loosing accuracy that much? Is it possible that I am just not getting the barrel clean enough in the first place (I can't see any obvious fowling in the bore, but the patches with bore cleaner never come out really clean for some reason)? Maybe I should just one or two evenings scrubbing it over and over with Shooter's Choice...


Please let me know if you have any suggestions.
I would also appreciate it if you post your own experiences with similar rifles and ammo... just wondering if my problems are unique...

Thank you.
Alex.

 

[BigG]

You have changed a lot of variables so it is very difficult to be scientific about the cause of the erratic accuracy. However, I would guess the bedding in the aftermarket stock. The gun has to have equal pressure on the bbl (or no pressure and the recoil lug has to be equally supported. Any variation on that will cause shot stringing. Might not hurt to glass bed the action (not the sides of the recoil lug -- where the the rear part bears.

Also, the screws that hold the action into the stock can cause erratic shooting. Sometimes you dink around with them and you'll find the sweet spot. HTH

 

[spacemanspiff]

first of all, how did the yugo shoot with turkish surplus BEFORE the modifications?
i'm by no means an expert with a rifle, but my stock yugo usually gets me about 5 moa at 100 yards, no matter if it is turkish, romanian, etc.

second, have you considered reloading so you have at least one constant type of ammo? there is quite a large variance in how hot turkish ammo is.

perhaps running a box or two of commercial 8mm would help you get an idea of what good ammo can do with it?

finally, how do you like that trigger? whats the range of pull weight you can have with it? i've been tossing around the idea of putting one in my yugo, the two stage heavy pull is starting to bore me.

about the only other thing i've thought about modifying is the stock, thinning out the hand grip a bit so my short stumpy fingers can get a better grasp on it, and maybe thin out where the support hand holds onto the stock as well.

but if i'm going to have that done, i may as well find a beat up yugo to do that to and have it drilled/tapped as well.

 

[Cosmoline]

You've got your scope mounted to a synthetic stock instead of the steel receiver?! I'd be amazed if you ever managed to get a good zero with that setup. My bet is your scope is getting kicked around on its mountings by the recoil.

 

[oldfart]

Mauser Accuracy Problems

I'm going through similar problems with a '93 Turk. I've had it for several years and it's never been much better than a 3 MOA shooter. Recently, I've been trying to make it better. Using the original stock, I carefully bedded the action and floated the barrel. I D&T for a scope and mounted a decent Bushnell on it, one that I knew was good.
At the range, with sandbags front and rear, I get about 3 MOA.
So I load up some "good" stuff and go back to the range. I still get 3 MOA.
Being exceptionally quick at deduction, I begin to see a pattern.
Back on the workbench, I push a plug into the barrel just ahead of the chamber and pour molten cerrosafe into said chamber. When it cools, I remove it and compare it to what an 8mm round is supposed to look like.
According to what I've read and experienced, best accuracy comes when the bullet is seated close to the lands of the bore. I don't think ANYBODY makes a bullet long enough to let me do that with this rifle. So now I'm faced with the prospect of removing the barrel, setting it back about thirty threads (more or less) and rechambering it. But if I do, I still have the original skinny military barrel which, when heated up, droops like a wet noodle.
I can either be satisfied with 3 MOA (which is plenty good enough for most hunting) or spend a couple of hundred on a new barrel. When you consider that I only paid $70 for the rifle, the idea of a new barrel takes a bit of getting used to. Sure, I could get a decent barrel in another caliber but I've got a ton of Romanian brass-cased surplus in my closet.
When we get these old war-horses, we tend to think we can win the Kentucky Derby with them. Well, they weren't made for racing, they were made for war. A 3 MOA shot at an enemy soldier is usually good enough to hit him. Similar accuracy at the range sucks. We can improve these old rifles; I know, I've done it, but it takes time and money. There isn't any magic formula either: Bed the action. Float the barrel. Keep the barrel cool when shooting, even if you have to wipe it down with a wet cloth. Carefully tighten the action screws, with a torque wrench, if necessary. Use hand-loaded ammo unless you can buy Federal Match fodder. Above all, be prepared to change barrels.
Good luck!

 

[BigG]

When we get these old war-horses, we tend to think we can win the Kentucky Derby with them. Well, they weren't made for racing, they were made for war.

This is so true, Oldphart!

I cannot tell you how many cut down M1917 Enfields, M1903 Springfields, Krags, etc. I've seen in the used gun racks for a song. Guys tried to make a silk purse out of a sow's ear or at least a war relic and made a mediocre hunting rifle they weren't satisfied with and denied a future generation familiarity with an actual piece of war materiel. Sad. Now when I see them destroying - um - customizing - the furrin surplus guns, it does not impact like it did the dear ole USA ones.

BTW, I noticed somebody mentioned the scope mounted to the stock??? - if your sight is not mounted rigidly to the barreled action, you will hardly get it to be consistently accurate.

 

[rbernie]

If you think that the decrease in accuracy is due to rapid fouling, I'd recommend giving the bore a couple of cleaning sessions with J-B Bore Cleaner followed by J-B Bore Bright. I have found that all of my MilSurps have benefited greatly from a thorough bore cleaning and polishing even when they looked shiny and bright.

If you think that the decrease in accuracy is due to heat, well, you're gonna have to do something about that stock.

And finally - every rifle has a preference for the weight/brand of ammo that it likes/dislikes. For example, my 1895 Chilean Mauser is very finicky about 140gr-150gr factory loads; it hates PMC Bronze and Win and Federal, but will lump 3-shot groups of Remington 145gr SP into one raggedy hole. This same rifle will also shoot most any brand of 170gr-175gr stuff equally well, although it likes S&B best. You just never know until you try...

IN short - it will aid your troubleshooting immensely to cycle thru small lots of ammo (all shot from a cold/clean barrel) to see what your rifle likes. Having established that as a baseline will make your susbsequent troubleshooting a LOT easier. Trust me on this.

 

[Cosmoline]

As I understand it, the scope sits on the plastic stock but is bolstered from below by a clamp on the barrel. It still strikes me as a good way to get your groups to get wider and wider as the firearm heats up.

 

[AlexI]

You have changed a lot of variables so it is very difficult to be scientific about the cause of the erratic accuracy. However, I would guess the bedding in the aftermarket stock. The gun has to have equal pressure on the bbl (or no pressure and the recoil lug has to be equally supported. Any variation on that will cause shot stringing. Might not hurt to glass bed the action (not the sides of the recoil lug -- where the the rear part bears.

Also, the screws that hold the action into the stock can cause erratic shooting. Sometimes you dink around with them and you'll find the sweet spot. HTH

I never seriously tested the accuracy of this rifle before the initial modifications, just put a few rounds through it for functional check and then put it into new stock. The following modifications (recrowning, new scope) were done one by one and didn't apear to seriously change anything.

Regarding bedding - as far as I could see, this stock does not touch the barrel forward of the receiver, with quite a lot of space left around it. Are there any articles/instructions available online about glass bedding action? Is it only the recoil lug that has to be bedded, or all contact surfaces?

Is there any method to "dinking" with the action screws? I thought they should be well tightened, anyway...

I thought about trying better ammo, too. I am not set up for reloading, and don't know if there is any match ammo produced in 8mm. What brands are considered accurate? Currently the only commercial 8mm I have at hand is maybe half a box of Igman SP. Can it be expected to be more accurate then surplus?

Now, the scope is actually mounted on the plastic rail, integral with the stock. There is a steel part clamped on the barrel under that rail, and the rail is bolted to it (approximately at the scout scope position), so it is not quite as bad as it looks. I have read some reviews that said scopes can stay reasonably stable on this mount.
What I really need to do is shoot a couple groups in the beginning of a shooting session, save the target, and don't touch the scope adjustments. Then come back with a cleaned rifle next time, shoot a couple groups, and compare with the saved target to see if the scope moved. Would that be a scientific approach?

Finally, I realize I am not going to get a "silk purse out of a sow's ear". All I hope for is 2MOA accuracy at best. And, this M48 was a common, beat up rifle with no war history (produced after WW2), so I didn't have any second thoughts about making a project gun out of it.
I wouldn't be surprised with poor accuracy, as long as it was stable. What bugs me is the fact that every time I go to the range, it goes from OK to bad (and there is no observable "stringing", which is expected if heat and poor bedding is to blame, right?). In one case, I didn't have time to clean the rifle properly after a relatively short shooting session (just washed out corrosive salts with Windex at the range). Came back next morning, and accuracy went bad right away. This is what makes me think it has to do with barrel fouling more then heat. Makes sense, doesn't it?
I am going to try "J-B Bore Cleaner followed by J-B Bore Bright" suggestion. At least it wouldn't hurt, and won't take too much time and money.


spacemanspiff, to answer your question about the trigger. I like it very much, it was easy to adjust (I think it is supposed to go 2 - 6 lbs), and even if you set it at the low limit, it doesn't cause accidental discharge when bumping the stock on the floor.

Alex.

 

[BigG]

"2 MOA accuracy at best" - that is better than a lot of rifles I've seen can do, seriously. All the guys claim 1 MOA - what that means I leave up to your imagination. It could mean that one time a gun shot less than one inch and all the rest of the times it shot 6" at 100 yds.

Usually the military requires them to shoot 3 MOA or thereabouts for acceptance. The M16 is a rarity in that it often shoots 1 MOA. But that is the only exception to the rule I know. Your typical bolt guns and semi autos shoot 3" or more with a good shot operating them.

The scope being mounted to the stock and then clamped to the bbl sounds like bad juju for accuracy. JMHO

Glass bedding is usually mostly around the recoil lug area, however, sometimes the whole action is bedded. The sides should not be glassed but the area that bears aft, like the recoil lug imho.

 

[AlexI]

"2 MOA accuracy at best" - that is better than a lot of rifles I've seen can do, seriously. All the guys claim 1 MOA - what that means I leave up to your imagination. It could mean that one time a gun shot less than one inch and all the rest of the times it shot 6" at 100 yds.

Well, then I really got taken with all those 1MOA boasts... and I should feel a whole lot better about my own shooting! I never doubted that under 2MOA shooting is common with almost any scoped bolt gun.
Funny thing is, I can shoot 2MOA and under groups with this rifle practically every time I come to the range - as long as these are the first groups that day. Now if I could make it last a little longer! Worst case, I will be patient and will get it zeroed based on these first shots. Then I will hopefully be able to expect decent accuracy for those first shots that really matter in real life... and at the range, I will just switch to shooting offhand at bigger targets when the groups start growing.

Alex.

 

[rbernie]

"2 MOA accuracy at best" - that is better than a lot of rifles I've seen can do, seriously. All the guys claim 1 MOA - what that means I leave up to your imagination. It could mean that one time a gun shot less than one inch and all the rest of the times it shot 6" at 100 yds

Well, I've got something to say about that.

My Mk4No1 Enfields will, from a sandbag rest, group PMP and Winchester 180gr softpoints and Federal 150gr softpoint factory ammo into five-shot groups of less than 1 1/2" (and will sometimes do better if my luck holds out) - over and over and over again.

My 7x57 '95 Mauser will, from a sandbag rest, group Remington 145gr softpoint factor ammo into five-shot groups of less than 1" (and will USUALLY do 3/4") - over and over and over again.

The key is that I took the time and effort to find out what ammo my MilSurps liked, and took the time to find out what ammo gave something closer to patterns than groups in these rifles.

That's not voodoo and that's not bullpoop. That's just common sense and a willingness to experiment and learn.

 

[spacemanspiff]

another question, have you chronographed the turkish ammo after all the modifications were done? i'm curious to see if theres a significant drop in velocity having the barrel cut and recrowned.

i've only chrono-ed some romanian '77 surplus, averaged 2,496 fps. if i come across any more turkish i'd like to chrono that, see just how hot they were making it.

i know you said you were shooting at 100 yards, but just for grins, what does it do at 25 yards? thats where i do the most of my shooting, between 25 and 50 yards, though i'm still on the iron sights. i get all kinds of enjoyment from shooting empty 12 guage shells wedged into the top of the target at 25 yards. if i can consistantly hit a target less than an inch wide and sticking out of the target 2 inches, i'm happy. even more happier when i realize that all the shots i thought were misses actually werent, the shell has 3 or 4 holes in it before getting popped out of the cardboard.

when i'm on a good day, with iron sights, i get 1 1/2 inch groups at 50 yards. i figure that to be 2moa, and very adequate for my shooting skills. i get 4-5 inch groups at 100, but i'm usually too lazy to walk my target out to 100, so i stick to 50.

 

[AlexI]

I don't have a chronograph, but would be surprised if there is a really bad drop in velocity with barrel shortened by just 1" or so.

I only shot the Mauser at 50 yards several times for groups (to begin sighting a scope in). I don't think any of them were bigger then 1.5", mostly around 1".
Other then that, I only shoot it at 50 yards standing (offhand) at things like approximately palm sized rocks (this is kind of a scout setup, after all, no sense in sticking to the bench shooting with it). Get them almost every time, even with degraded accuracy. And there is a cool visual effect as the rock gets pulverised by a hit with an 8mm bullet! Interestingly, when the same kind of rock is hit with a 7.62x39 bullet from AK, it usually just gets broken in two or several big pieces, or simply thrown aside.

Alex.

 

[Okiecruffler]

I don't think 2MOA is asking too much out of an M48. I have 2 in my collection right now that will shoot 1.5" groups with Turk ammo. Of all the others I've had I can only think of one that wouldn't shoot 2MOA, and a recrowning fixed that. It may be an ammo problem. That Turk ammo, on top of being the most corrosive stuff ever made, is pretty dirty. When shooting for groups I always clean the bore after every 5 shot group.