Rifle Accurate at 25, 50 yards, not at 100

[8MM Mauser]

Hey guys I thought I might run a rifle question past the board:

I have a "Sporter" Mauser which is my primary gun for hunting big game. If you remember I was on here a few months ago asking questions about my Simmons scope. However, after shooting over 100 rounds of the same ammo I have figured out this is not likely a scope problem.

Last Sunday I took my rifle out, and because I was going to be re-zeroing I first set-up at 25 yards. I shot a five shot group - about two inches low-left, holes all touching. So i backed out to 50 yards and repeated... a five shot group, about 1 inch low left and a group you could cover with a quarter.

So I am feeling pretty good at this point, expecting that my real problem before was a bad ammo problem (I was shooting reloads - for this test I switched to PPU). So I back it out to 100 yards and shoot another five shot group... No hits on paper. So i shoot another five shot group, adjusting my aim slightly up and to the right... no hits on paper. All 20 shots were with the same ammo, and off of the same lead-sled I kept dragging all over the range.

So i go back to 50 yards... and I shoot a similar group as the first time I shot at 50 yards. (not quite as tight, I was frustrated at this point, but still a solid group right near the bull.)

My question is: How am I getting this much variation from 50 to 100 yards? How can my rifle put up tight groups at 50 and miss paper at 100? Last I checked it was sighted at 100 yards... This is a very OLD gun, it was a Gewehr that was given to the Turks after WWI. It still has the original barrel (or at least the barrel it was imported with - probably 50 years old at best). Is this a problem that results from wear? I have a stock Czech Mauser from 1934 that I can keep on a paper plate at 100 yards with those crappy iron "sites."

This is a very strange problem to me. I am not sure how to proceed. The method described above has always been my sight-in method and it has always worked well. If I can't figure this out by November I will be hunting with a stock VZ24.

Any help is much appreciated.

[T. O'Heir]

Has it ever been 'on paper' at 100? You shooting off a bench? It can still be a scope mount issue too. You bore sight it?
Start by putting a great big hunk of paper behind the 100 yard target. That'll tell you where the shots are actually going.

[8MM Mauser]

Yes, I've been shooting it for 7 years, and it has been my main hunting rifle for three years now and it has always achieved a good group at 100 yards once sighted properly (and assuming I did my part). I usually start at 25, move to 50, then move to 100 when sighting in for a new cartridge... which is exactly what I did here... Except it didn't hit anything at 100 when it was landing solid groups at 25 and 50. Same process different results. I had a man sized hunk of cardboard behind the target for just the reason you describe too sir.

The scope didn't seem loose or wiggly - and I have had that issue before.

[T. O'Heir]

Hi. Simmons stuff isn't high end kit. That's why Savage quit using 'em on their package rifles. Had a Tasco that worked just fine, then quit. Put a bore sight on and every time I opened and closed the bolt, the reticle would move left or right. Might be that or it might be a bedding issue.
The inside of the stock, especially the barrel channel sealed? If it isn't you might be seeing the result of the stock swelling in the barrel channel due to moisture in the air. Check the channel by running a dollar bill(have to remind myself there still is such a thing Stateside. snicker.) under the stock to the chamber area and looking for any contact between the barrel and stock.
Assuming all stock screws are tight and it has a floated barrel.

[Rancid]

What is the group at 75 yards?

[8MM Mauser]

Thank you I will try that.

[elmbow]

have you slugged the barrel? Read up on how to slug using egg sinkers and slug it, see what you come up with. If you are getting good groups at fifty, I doubt it is an oversized bore but.......it's worth checking. Are you getting any keyholing on your target?
I would get rid of the Simmons scope no matter what, spend at least $200 on a scope. Double check your bases and rings, but this doesn't sound like a scope or scope mount problem, you are too consistent on paper. The barrel could be oversized and sending them off on a tangent beyond fifty yards. And another thing, adjust your scope at fifty so you are hitting where you're aiming. Make sure you are shooting consistently.
Also, read up on the 8mm history, there were two bore diameters, a .318 and .323 IIRC. Have never owned one but remember reading precautions on the early 8mms.

[jmr40]

Use a larger target at 100 so you can see where you are hitting. Until then you are just wasting ammo and guessing.

[johnwilliamson062]

If you aren't getting keyholes...

Shooting off a bench without a sling at all three distances?
Bean bags, shooting sled, off your fist?
I had a rifle I shot off a bench at 50 as shooting prone would have required laying on the shooting bench, then set-up properly prone with a sling and everything went haywire. Tension on the sling pulled the stock into the barrel. Not enough to take it off paper though.

Is the load you are shooting at a much greater velocity or wit a much different weight bullet than the other loads? Your twist rate may not match your current load.

[Snyper]

I'd be adjusting the scope to get the point of impact centered left and right instead of adjusting the point of aim to compensate.

It should also be hitting high at 50 yds to be closer at 100

I don't think the gun nor ammo are as much the problem as the method of sight in.

With a Simmons (or really any optical sight) there are probably also some parrallex issues causing the POI in relation to POA to differ at varying distances

[jmr40]

It should also be hitting high at 50 yds to be closer at 100

Many rifles will still be low at 50 yards for a 100 yard zero, especially with optics. The bore is about 1.5" lower than the center of the scope. The muzzle is at a very slight upward angle and the bullet is still rising at 50 yards. Sometimes at 100 yards. At some point it reaches it's apex and starts dropping.

[Colorado Redneck]

I had a similar issue with a 22-250. When I bought the gun (used) it was fine and would shoot tight groups at 250 yards. A couple years later, it would shoot fine for groups at 100 yards, but at 250--it was a "pattern" more like a shotgun shooting buckshot. Gun shop guy suggested I try a different bullet before getting rid of the gun. Presto! Worked like a charm. For some reason, the bullets I had been using were no longer stabilized out to 250 yards. Never figured that one out. But going to a different grain and shape of bullet solved the problem.

Perhaps the rifling close to the chamber is getting eroded and the bullet is getting snagged on a rough throat, causing the projectile to become unstable as it loses velocity.

[1stmar]

Assuming the paper is at least 11x7, and you are center punching 1" groups at 50 repeatedly, I don't think the scope itself is the issue. I agree see what is happening at 75yds, check parallax. Put a bigger piece of paper out at 100 or fresh cardboard on the target.

[8MM Mauser]

have you slugged the barrel? Read up on how to slug using egg sinkers and slug it, see what you come up with. If you are getting good groups at fifty, I doubt it is an oversized bore but.......it's worth checking. Are you getting any keyholing on your target?
I would get rid of the Simmons scope no matter what, spend at least $200 on a scope. Double check your bases and rings, but this doesn't sound like a scope or scope mount problem, you are too consistent on paper. The barrel could be oversized and sending them off on a tangent beyond fifty yards. And another thing, adjust your scope at fifty so you are hitting where you're aiming. Make sure you are shooting consistently.

I will look into that thank you.

[8MM Mauser]

If you aren't getting keyholes...

Shooting off a bench without a sling at all three distances?
Bean bags, shooting sled, off your fist?
I had a rifle I shot off a bench at 50 as shooting prone would have required laying on the shooting bench, then set-up properly prone with a sling and everything went haywire. Tension on the sling pulled the stock into the barrel. Not enough to take it off paper though.

Is the load you are shooting at a much greater velocity or wit a much different weight bullet than the other loads? Your twist rate may not match your current load.

No keyholes - all groups were shot off of a lead-sled while lying prone. I was shooting all the same ammo. That is an interesting case though, I will try and think if I changed anything on the 100 yard shots.

[8MM Mauser]

With a Simmons (or really any optical sight) there are probably also some parrallex issues causing the POI in relation to POA to differ at varying distances

Many rifles will still be low at 50 yards for a 100 yard zero, especially with optics. The bore is about 1.5" lower than the center of the scope. The muzzle is at a very slight upward angle and the bullet is still rising at 50 yards. Sometimes at 100 yards. At some point it reaches it's apex and starts dropping.

Use a larger target at 100 so you can see where you are hitting. Until then you are just wasting ammo and guessing.

Assuming the paper is at least 11x7, and you are center punching 1" groups at 50 repeatedly, I don't think the scope itself is the issue. I agree see what is happening at 75yds, check parallax. Put a bigger piece of paper out at 100 or fresh cardboard on the target.

Interesting - I think I will have to try that, i'll get one of the large boxes we use at work and lay that against my target stand and go from there.

[8MM Mauser]

I had a similar issue with a 22-250. When I bought the gun (used) it was fine and would shoot tight groups at 250 yards. A couple years later, it would shoot fine for groups at 100 yards, but at 250--it was a "pattern" more like a shotgun shooting buckshot. Gun shop guy suggested I try a different bullet before getting rid of the gun. Presto! Worked like a charm. For some reason, the bullets I had been using were no longer stabilized out to 250 yards. Never figured that one out. But going to a different grain and shape of bullet solved the problem.

Perhaps the rifling close to the chamber is getting eroded and the bullet is getting snagged on a rough throat, causing the projectile to become unstable as it loses velocity.

I feel like that may be possible here - it is strange because I used these same rounds a few years ago and they were great. My barrel is getting quite aged though; and I have shot this gun quite a lot for what it is.

I will have to take a good hard look down the bore I think.

[8MM Mauser]

Thank you all for the advice - I have many things to try now.

[Pathfinder45]

While you are at it, clean the bore thoroughly using a good copper solvent, then do it again.

[Mobuck]

I would question why you kept shooting with an off kilter zero rather than center the POI at 25 or 50?