Sudden group changes

[robtattoo]

Long story short:
I'm trying to work up a load for an old, 1947 Mauser that has been rebarreled to .257 Bob.
I've only been to the range with it 3 times now (2hr round trip)
First time shooting old factory ammo to dial in the scope. 120gn ammo into neat 1" groups, 100s into 1.5

Second to try some reloads. I didn't have a "recommended" powder but found a load for what I had (imr4064). 100gn Core Lokt bullets into 1.5" + groups

Yesterday. I got hold of a jug of THE recommended powder (imr4350) & loaded up the 100gn partitions I actually want to shoot. Terrible. Best 'group' was maybe 4" with zero consistency.

Could a powder & bullet change really affect things THAT badly?

I'm probably going to pull the stock & scope anyway, then try another scope just in case, but just want confirmation that a load couldn't be THAT bad all by itself. Could it?

 

[MuleyFever]

I am messing with my wifes 7mm-08. Getting 3"+ groups from different charge weights using one bullet powder. Switched the bullet/powder and got sub 1" groups.

 

[5MilesBack]

The changes could absolutely have a drastic effect on accuracy........that's why a bunch of guys reload.......to come up with loads that shoot best in each rifle. The other thing......did you clean the rifle at all between your sessions? Some rifles like a clean barrel, some don't.

 

[Bearlodge10]

Short answer is that yes, powder and bullet change can make a difference... A step or two further and probably more accurately is that different powder with same primers can get drastically different results. I have messed with a few different powder/ primer combinations trying to replicate commercial loads. 4350 is one that I have used magnum primers with to get better results.
For the record I have found IMR 4831, Reloder 22 and varget to be good with my Bob and the bullet weights listed.

 

[Cahunter805]

A powder/bullet change could be that drastic. What charge weights did you try? What OAL are you loading to? Obviously you know the rifle is capable of 1”-1.5” groups.
Swapping scopes and checking to make sure everything is tight is a good idea to help eliminate those variables also.

 

[robtattoo]

A powder/bullet change could be that drastic. What charge weights did you try? What OAL are you loading to? Obviously you know the rifle is capable of 1”-1.5” groups.
Swapping scopes and checking to make sure everything is tight is a good idea to help eliminate those variables also.

I loaded to book length (2.770") with charge weights from 43 to 45.5gn.

The last loads I tried I seated much longer (2.90") but I figured that this time, I'd go strictly by the book. I'll admit, I had complete analysis paralysis on COAL. For the life of me, I absolutely couldn't remember or figure out why it would make a difference (I've only need reloading 12 years.....)

I checked the action bolts & ring screws at the range & they were fine. Obviously I can't prove the scope without switching it into another rifle, but it's been going strong for 40 years & I've done nothing that would have caused it to just fail.

 

[Cahunter805]

257 Roberts Load Data

Explore the world of Nosler, renowned for crafting the finest bullets, ammunition, rifles, and brass. Discover our extensive lineup, including Partition, AccuBond, E-Tip, Ballistic Tip, Custom Competition, and more. Experience superior quality and performance with Nosler products.

www.nosler.com

This Nosler data shows 43.5 as max with 39.5 most accurate.
Also since you have 4064 you could try a set of handloads with that to see if It produces better groups.

 

[robtattoo]

257 Roberts Load Data

Explore the world of Nosler, renowned for crafting the finest bullets, ammunition, rifles, and brass. Discover our extensive lineup, including Partition, AccuBond, E-Tip, Ballistic Tip, Custom Competition, and more. Experience superior quality and performance with Nosler products.

www.nosler.com

This Nosler data shows 43.5 as max with 39.5 most accurate.
Also since you have 4064 you could try a set of handloads with that to see if It produces better groups.

Nosler data for the .257 is suuuuper low. For some reason they've never updated for modern actions & +P loadings like everyone else.
Looking online, a very common recommendation (seems like almost a universal load) is 45gn of one of the 4350s
4064 didn't give good velocities. Certainly not what I'm looking for. I'm aiming for 3000fps, which is well within the limits.

 

[Billogna]

There's a lot of missing info, like your barrel length, profile and twist rate, But the short answer is Yes. Different powders can have a PROFOUND impact on grouping due to bullet construction/type and burn rate. And from the load data I've looked at 3000fps was pretty close to max velocity with 100 grain bullets. Accuracy loads were running closer to 2900. And that barrel may just prefer heavier pills if those 120 grainers were grouping 1 inch.

 

[Cahunter805]

Nosler data for the .257 is suuuuper low. For some reason they've never updated for modern actions & +P loadings like everyone else.
Looking online, a very common recommendation (seems like almost a universal load) is 45gn of one of the 4350s
4064 didn't give good velocities. Certainly not what I'm looking for. I'm aiming for 3000fps, which is well within the limits.

Seems some load data shows up to 47gr of 4350. You might find accuracy at the higher charges. If your set on 3000 and only have 4350 then that’s what I’d suggest.

 

[robtattoo]

Seems some load data shows up to 47gr of 4350. You might find accuracy at the higher charges. If your set on 3000 and only have 4350 then that’s what I’d suggest.

It's another one of those chamberings that I somehow seem to be magically drawn to, where load data is all over the damn place.
Kinda makes me wish I could've just been happy with a .308 sometimes.....

 

[robtattoo]

There's a lot of missing info, like your barrel length, profile and twist rate, But the short answer is Yes. Different powders can have a PROFOUND impact on grouping due to bullet construction/type and burn rate. And from the load data I've looked at 3000fps was pretty close to max velocity with 100 grain bullets. Accuracy loads were running closer to 2900. And that barrel may just prefer heavier pills if those 120 grainers were grouping 1 inch.

It's a 23" standard sporter profile (I couldn't give you a number, don't know the maker) with a standard 1:10 twist. Theoretically with that ROT it should handle everything from 87s to 120s. Maybe it does just do better with the heavier bullet, but the bearing surface on the 100gn NPTs is near as damn it the same as the Speer 120s I pulled down from a factory load (for some reason, 1 round out of the box wouldn't chamber so I tore it down to see why) so I can't imagine it's an issue.
I'm going to try seating them out longer for a go around & see what happens. I just can't believe it's the bullet powder combo alone. It's kinda a classic loading for the cartridge.

Assuming the action, mounts & scope are all OK, of course.

 

[OXN939]

Could a powder & bullet change really affect things THAT badly?

Absolutely. Biggest thing I've learned from reloading- if you get a group like that, it's valuable information telling you that you need to change a major component. 4" groups mean your rifle doesn't like that combo, and it's not likely that tweaking seating depth/ powder charge volume is going to do much.

 

[Billogna]

It's a 23" standard sporter profile (I couldn't give you a number, don't know the maker) with a standard 1:10 twist. Theoretically with that ROT it should handle everything from 87s to 120s. Maybe it does just do better with the heavier bullet, but the bearing surface on the 100gn NPTs is near as damn it the same as the Speer 120s I pulled down from a factory load (for some reason, 1 round out of the box wouldn't chamber so I tore it down to see why) so I can't imagine it's an issue.
I'm going to try seating them out longer for a go around & see what happens. I just can't believe it's the bullet powder combo alone. It's kinda a classic loading for the cartridge.

Assuming the action, mounts & scope are all OK, of course.

That 4350 might be just a hair slow for those bullets in your gun. The bearing surface may call for just a bit more pop. I'll second trying the 4064 with the partitions and see what happens. But what was the factory ammo you were shooting?

 

[robtattoo]

That 4350 might be just a hair slow for those bullets in your gun. The bearing surface may call for just a bit more pop. I'll second trying the 4064 with the partitions and see what happens. But what was the factory ammo you were shooting?

It was some very, very old mixed Winchester. I verified that, at the time, they were using Speer 1410 bullets in that load. I do have a couple hundred on hand, so that might just be the way forward.
I'm really struggling to believe that a load that is so popular, with so many people just isn't going to work.
I bought the 4350 especially for it, too.

 

[Bubblehide]

First, the advice above is good sound advice.

Long ago I had a friend with a similar issue. We check everything and found no issues. I took the gun and removed the scope, in doing so I found one screw that snapped off about have way along the threads. So there were enough threads to catch and make it appear that nothing was wrong. Drill it out, re-tapped it and remounted the scope, problem solved.

I am not saying that that is your issue, but if powder and proper seating depth do not fix it, I would be looking for something like the above.

 

[gbflyer]

Can you go back to your baseline factory ammo and verify? That would eliminate a mechanical issue, unless of course it’s heavy barrel fouling which is a whole ‘nuther can of worms with opinions.

 

[robtattoo]

Can you go back to your baseline factory ammo and verify? That would eliminate a mechanical issue, unless of course it’s heavy barrel fouling which is a whole ‘nuther can of worms with opinions.

I have 3 rounds of factory ammo left. It wasn't the most accurate I had, but it would give me a baseline. Good thinking.

 

[Billogna]

It was some very, very old mixed Winchester. I verified that, at the time, they were using Speer 1410 bullets in that load. I do have a couple hundred on hand, so that might just be the way forward.
I'm really struggling to believe that a load that is so popular, with so many people just isn't going to work.
I bought the 4350 especially for it, too.

I hear ya there!! That 4350 is scarce enough these days. But I'll share this. I made a mistake with my .308 chasing a certain velocity and ended up wasting a LOT of components instead of just listening to the gun. There was nothing wrong with the gun. It would group fine with slower combos but no matter what I tried it wouldn't group with what I wanted for it .....150 grains at 2950 or better. Sometimes they just is what they is...

 

[WCB]

I have had two factory loaded rounds same bullet weight same velocity and same basic bullet shape. 8" difference in POI and different group sizes. If I remember right one was around MOA the other was 3moa ish. So in short yep definitely can happen.