Bullet jump?

[Alderman]

After reading about different bullets liking different “jumps” I am left with a question.
Do all gun makers try to make their guns the same dimensions?

Such as if I have two 30.06 guns Winchester is it reasonable to expect the dimensions to be the same?

Would a Remington or some other manufacturer 30.06 change dimensions by design?

I know there would be some slight variation due to tooling wear so no two are exactly alike but do they purposely change chamber dimensions for some reason?


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[DrMike]

It is my understanding that chambers are manufactured to SAAMI dimensions with allowance for tooling, wear, etc. Thus, the major manufacturers do not alter chamber dimensions by design. A custom cut could include such adjustments.

 

[Alderman]

It is my understanding that chambers are manufactured to SAAMI dimensions with allowance for tooling, wear, etc. Thus, the major manufacturers do not alter chamber dimensions by design. A custom cut could include such adjustments.

Mike. Would you happen to know if manufacturer’s loading data takes into account the ideal jump when they design the bullet and print their tested OAL?


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[Alderman]

It is my understanding that chambers are manufactured to SAAMI dimensions with allowance for tooling, wear, etc. Thus, the major manufacturers do not alter chamber dimensions by design. A custom cut could include such adjustments.

Mike. Would you happen to know if manufacturer’s loading data takes into account the ideal jump when they design the bullet and print their tested OAL?

I’ve done a lot of loading over the years and usually just start with the printed OAL. I have done some testing with adjusting OAL but I have usually gotten suitable hunting application results without having to.




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[DrMike]

Again, it is my understanding that testing procedures seek to adhere to SAAMI parameters. This means that the loads themselves are built to meet SAAMI parameters. Thus, jump will be consistent given the parameters adopted.

This is the reason a hand loader is responsible to make his/her own tests to verify that a given load is safe given the firing system that hand loader is using. Published loads will be safe in the firing system used. This is why it is a good practise to carefully read all the parameters published with the load rather than accepting the charge weights alone.

 

[mjcmichigan]

Just like mass produced bullets.. these assembly and machining operations are set for knocking out a bunch of parts.
Maybe they have 10 lines making barrels.
The tooling across the ten, while designed to same spec will have different degrees of wear and tear on them. Also, likely different people set them up. So maybe one measures different from a co worker and boom, two 3006 coming off side by side lines and there are differences you can measure in the 0.0xx range.

SAAMI established minimum dimensions. That’s so ammo makers can be confident the ammo chambers.

I had a box of 3006 corelokts, and when I lined them up on the table, you could see lots of variations in OAL. Rifles are the same.

If you have two rifles same make and caliber, I’d hope you could use the same ammo, but I could easily see you might find differences in performance.. fast barrel, slow barrel… even more so if made in different plants or years.


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[ozarkpugs]

You have to check the bullet jump for each bullet you load . One brand 180 grain bullet may have a . 020 jump at a given OAL and a 180 grain bullet of a different brand may be crammed tight or . 040 out at the same OAl .That is because different shaped bullets of the same weight have the ogive at different places on the bullet . Most chambers are sized for the longest cartridge base to ogive length you are likely to encounter .

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[ShadeTree]

Alderman, you're kind of asking 2 different questions. Chamber dimensions, and bullet jump.

Far as actual chamber dimensions, that's held to a pretty tight tolerance and is designed as Mjcmichigan stated, so that factory ammo always chambers. The largest allowable cartridge dimension will always chamber in the smallest allowable chamber.

Conversely if a smallest allowable cartridge dimension is fired in a chamber at maximum allowable specs, it still will be safe and not have excess headspace.

Bullet jump from chamber to chamber within the same cartridge, is a whole other matter. Seen it again and again.

I just recently checked that Sauer 30-06 I just purchased, and using the same 180 gr core lokt bullet that I used to check a Savage 111, it has a .070 longer throat, or free bore.

In other words with that bullet, the bullet was into the lands on the Savage at an O.A.L of just 3.190. Short throat. In this rifle it's into the lands at 3.260.

Factory loads by the way with that bullet were loaded right at 3.190. The Savage hated the factory length, but other than that it caused no issues.

I have a M70 that on most book length loads, I'd have to bear down to get the bolt closed if I loaded at that length. I gotta load WAY shorter.

 

[Wis65x55]

Why then can I load ammo 3.55" for my 300 WM and not touch the lands on a new factory rifle?

 

[ozarkpugs]

Why would you think you would not be able to with some bullets ? People confuse OAL with CBTO length . The OAL determines if it will fit in the magazine the base to oglive length determines how much if any bullet jump . It is possible for one bullet of a certain weight to be crammed into the rifling at a OAl of 3.55 while another bullet of the same weight but different shape have a jump of several . 000 at 3.55 OAl .

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[TXbaldhunter]

Every rifle is different no matter who the manufacturer is.As for bullet jump,I usually find good accuracy between .025 - .100 off the lands.There again,depends on the rifle and the bullet,they are different too and can vary a little from lot to lot as well.I have some rifles that when the cartridges are loaded to the full mag box length,the bullets still won't touch the lands,I have some rifles that the bullet will touch the lands well before it reaches the mag box length.

 

[SJB358]

Why then can I load ammo 3.55" for my 300 WM and not touch the lands on a new factory rifle?

300 Win has a long throat. The standard SAAMI throat is actually very well suited to long pointy bullets, if it is able to stretch out to 3.6".

 

[ShadeTree]

Why then can I load ammo 3.55" for my 300 WM and not touch the lands on a new factory rifle?

300 Win has a long throat. The standard SAAMI throat is actually very well suited to long pointy bullets, if it is able to stretch out to 3.6".

Scotty, you are correct, the 300 WM's come through with a long throat. You're more of a magnum man than me, but I'm just going off the different magnum cartridges I worked with. I think magnums in general are built with a generous free bore.

 

[seokladuckin]

Seen a new 700 Remington 3006 that a 180 bullet would not reach the lands .

And was the worst shoot 700's I ever saw .

He sent it back.

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[gbflyer]

Good info here.

The throat also begins to erode starting with fired round #1. Some go quicker than others, depending on how much powder it’s burning in relationship to the bore diameter.