Back Bored rimfire barrel

[Pyscodog]

Ser num AY is 1982 . If thats your prefix, hard to tell with the glare . Excellent gun , great deal

Serial starts with AV. What I'm calling a button, your calling a lever, my bad and thanks for your help. I can now remove the bolt.

 

[Ggmac]

heres a copy of dates

 

[longbow]

All in all...nice gun.Should have fun shooting it. 22 Silo is a fun sport,did it for afew years with a 1712 ......

 

[Ggmac]

I would purchase some headspace shims from Numrich, just in case , and the shims will not be available forever . Ive bought a few sets , just in csae and it makes it possible to adjust headspace for individual lots of ammo

 

[Pyscodog]

Apologies Ggmac, it is AY. Letters are so small even with my specs they are hard to read.

 

[Hi-NV Shooter]

I would purchase some headspace shims from Numrich, just in case , and the shims will not be available forever . Ive bought a few sets , just in csae and it makes it possible to adjust headspace for individual lots of ammo

I have owned 5 of these rifles, and still own 2 and never needed to adjust headspace for different ammo. I am wondering how much difference would you need to measure before needing to adjust the HS
and how much of an improvement would you see on paper if you did.

Lee

 

[Ggmac]

I have owned 5 of these rifles, and still own 2 and never needed to adjust headspace for different ammo. I am wondering how much difference would you need to measure before needing to adjust the HS
and how much of an improvement would you see on paper if you did.

Lee

You wont know the possibility of improvement until you try . In my one gun thst I shoot alot , the accuracy can improve greatly IF that lot of ammo is on the tight side . You can learn alot about ammo and its peculiarities with trying . I usually shoot at 100 ,200 and 300 yds . The improvements really are seen at the extended ranges . You probably will not see any measurable difference at 50 .
having the shims now prevents me from searching for them in the future. They are cheap insurance . These guns are sure to outlast me , Im just a caretaker , having spare parts can only help the next caretaker.
I usually have the headspace at 44 but 43 has helped on some , 45 help some old cheap russian target ammo shoot excellent.

 

[Hi-NV Shooter]

You wont know the possibility of improvement until you try . In my one gun thst I shoot alot , the accuracy can improve greatly IF that lot of ammo is on the tight side . You can learn alot about ammo and its peculiarities with trying . I usually shoot at 100 ,200 and 300 yds . The improvements really are seen at the extended ranges . You probably will not see any measurable difference at 50 .
having the shims now prevents me from searching for them in the future. They are cheap insurance . These guns are sure to outlast me , Im just a caretaker , having spare parts can only help the next caretaker.
I usually have the headspace at 44 but 43 has helped on some , 45 help some old cheap russian target ammo shoot excellent.

Interesting, I would think if adjusting the HS on a H&R M12 improves the accuracy, it would work for any other rifle and not just the M12. also I am puzzled by the accuracy improvement would only be noticeable at distances beyond 50 yards I assume you meant.
it is the exact opposite of what I have seen and experience, outstanding accuracy at 50-yards generally extends to 100 yards. can't say about anything farther out as I don't shoot past 100 yards.
here is an example-
50-yds. 10-shot group and 100-yds. 3-shot group

Lee

 

[Ggmac]

Interesting, I would think if adjusting the HS on a H&R M12 improves the accuracy, it would work for any other rifle and not just the M12. also I am puzzled by the accuracy improvement would only be noticeable at distances beyond 50 yards I assume you meant.
it is the exact opposite of what I have seen and experience, outstanding accuracy at 50-yards generally extends to 100 yards. can't say about anything farther out as I don't shoot past 100 yards.
here is an example-
50-yds. 10-shot group and 100-yds. 3-A

Almost all of my data is from those ranges and shot with 10 round groups . Sometimes Id shoot 500-1000 rounds making only one change . The rifle data I was getting at 50 was hard to measure as all-it does is make a larger ( slightly ) hole . The longer distance was a necessity and made getting data easier .
I think it does work on other rifles , the reason I used this model 12 was that It is extremely accurate and you could easily adjust headspace. Not all rifles are easily adjustable. The only other rifle I tested was heavily modified Cugir . It showed improvement along the same lines . But shooting and testing one change at a time ,using so much ammo of one lot and comparing it to another lot takes alot of time and resources.
more after coffee and walk the dogs
Gary

 

[Ggmac]

Just a quick note on headspace. Dont forget .001 one way or the other will cgange the engraving. Could give more fp protrusion ( depending on design )
While collecting data , you get the usual bell shape curve , i omit the hi and low and just use the most under the curve . Some of those groups were wallet show off groups but not a true representation of accuracy’

 

[Hi-NV Shooter]

Just a quick note on headspace. Dont forget .001 one way or the other will cgange the engraving. Could give more fp protrusion ( depending on design )
While collecting data , you get the usual bell shape curve , i omit the hi and low and just use the most under the curve . Some of those groups were wallet show off groups but not a true representation of accuracy’

Now engraving is something I experimented with and can say I have with my rifles never seen any change with just a 0.001 + or - change of engraving. now speaking in reference to Lapua ammo, I have measured as much as a 0.035 difference in bullet OAL as measured from the Ogive/first driving band in some of the lots I have and they still shoot equally as well between rifles. but I am using the Nevius chamber so this may be why.
correct me if I am wrong, but HS on a rimfire is taken from between the bolt face and rear of the shell casing or back facing of the rim.
so help me understand, how changing the HS will change engraving since once the front part of the rim is seated against the breech face it can not go any further in?
firing pin indentation can be altered with HS changes.

Lee

 

[Tim Slater]

COrrect me if I am wrong, but HS on a rimfire is taken from between the bolt face and rear of the shell casing or back facing of the rim.
so help me understand, how changing the HS will change engraving since once the front part of the rim is seated against the breech face it can not go any further in?
firing pin indentation can be altered with HS changes.

Lee

Lee,

That's true if the bolt fully chambers the cartridge. But what if the case rim is thinner than the headspace? Surely then, the bolt will only chamber the cartridge so far before it locks into battery.

 

[DGP4]

I tend to agree with Lee. Unless the chamber is cut to allow engraving (most are not) no amount of shims is going to cause the bullet to engrave. In other words, unless you have a true match chamber, engraving will not happen.

 

[Tony K Harper]

Lee,

That's true if the bolt fully chambers the cartridge. But what if the case rim is thinner than the headspace? Surely then, the bolt will only chamber the cartridge so far before it locks into battery.

Tim you hit the nail on the head. Matter of a fact the bolt can't fully seat the the rim to the barrel face. There is so much variance in rim thickness some rounds would be smashed when the bolt closed. That is why we have "headspace". The headspace always has to be larger than the rim thickness. The question really is how much larger? That depends on the ammo/lot you plan to shoot. Eley normally runs about .038 -.039. Lapua about .039- .0405. Generally, you need a little more headspace for Lapua to ensure you aren't crushing the head and having hard bolt closing.

With all this said, I still haven't answered the question of how much headspace do we need.

Years ago Time Precision made rifles that had easily adjustable headspace, and I spent years and a lot of money adjusting headspace.

I would sort my ammo by rim thickness then adjust the headspace accordingly. I tried everything from slightly crushing the head to so far out the round wouldn't fire. I never found the answer. The only thing I learned was too little headspace doesn't work as well as more headspace.

As a matter of fact as long as the rifle fires 100% of the time you don't have too much headspace. But if the bolt is hard to close on some rounds you don't have enough.

There was a time in RFBR .042 was considered the best headspace, then it went to .043. Now most are using .044 or greater.

The takeaway from all of this should be if some rounds chamber harder than others you don't have enough headspace for that brand or lot of ammo.

I'll also suggest a little test. Try pushing the round all the way to the barrel face with your thumb and shoot groups. Then just push the round in the chamber and let the bolt push it the rest of the way and shoot groups. You may be surprised.

TKH

 

[Tony K Harper]

I tend to agree with Lee. Unless the chamber is cut to allow engraving (most are not) no amount of shims is going to cause the bullet to engrave. In other words, unless you have a true match chamber, engraving will not happen.

Although some chamber reamers come with a depth stop you don't have to use it. The chamber and leade angle will be the same regardless of how deep the chamber is cut. The shorter the chamber the more the engraving.

TKH

 

[Ggmac]

1 you dont segregate your ammo , either by rim or to first band
2 my chamber engraves the bullet on most match ammo , we were talking about the m-12 weren’t we
3 if you measure your ammo and see that much difference, why would you not segregate it ? Why then measure it ?
If you dont believe it , dont base well it doesnt work because I haven’t tried it .
I think Bill Calfee had something to say about this . Not sure it was him .
We try to make EVERTHING uniform , why not adjust headspace to match ammo ?
Try it , but at long ranges , 20 shot groups , min of 5 , prefer 10 , eliminating the highs and lows , remember the bell shaped curve .
Come back and give data , after 10,000 to 20,000 rounds dont just guess because you havent tried it .
Dont you think a little extra pressure holding the entire rim against the chamber , uniform ( pressure) all the way around would have an effect on accuracy or harmonics dont try it . It does cost money and time . Maybe tuners don’t work either , I mean after all , its just harmonics , pressure , barrel time , etc

 

[Ggmac]

Tim you hit the nail on the head. Matter of a fact the bolt can't fully seat the the rim to the barrel face. There is so much variance in rim thickness some rounds would be smashed when the bolt closed. That is why we have "headspace". The headspace always has to be larger than the rim thickness. The question really is how much larger? That depends on the ammo/lot you plan to shoot. Eley normally runs about .038 -.039. Lapua about .039- .0405. Generally, you need a little more headspace for Lapua to ensure you aren't crushing the head and having hard bolt closing.

With all this said, I still haven't answered the question of how much headspace do we need.

Years ago Time Precision made rifles that had easily adjustable headspace, and I spent years and a lot of money adjusting headspace.

I would sort my ammo by rim thickness then adjust the headspace accordingly. I tried everything from slightly crushing the head to so far out the round wouldn't fire. I never found the answer. The only thing I learned was too little headspace doesn't work as well as more headspace.

As a matter of fact as long as the rifle fires 100% of the time you don't have too much headspace. But if the bolt is hard to close on some rounds you don't have enough.

There was a time in RFBR .042 was considered the best headspace, then it went to .043. Now most are using .044 or greater.

The takeaway from all of this should be if some rounds chamber harder than others you don't have enough headspace for that brand or lot of ammo.

I'll also suggest a little test. Try pushing the round all the way to the barrel face with your thumb and shoot groups. Then just push the round in the chamber and let the bolt push it the rest of the way and shoot groups. You may be surprised.

TKH

Sounds good but what if you’re on the fence , meaning theres got to be a spot ( headspace) where it becomes affects reliable ignition, or case crushing , hard bolt closure . When having the option of adjustable headspace, take it . Some guns will also be changing firing pin protrusion, it depend on how the bolt was designed .
Did you fire at long range , 100 , 200,300 ?
did you shoot min 10 round groups , 20 if time permits
Did you eliminate the highs and lows ? ( bell shaped curve )
Did you check and note different velocity with different headspace . This would of been something I should of checked first , it was telling and COULD account for the accuracy differential.
if i were to just shoot at 50 or even 100 , and used 5 round groups, the testing would of been easier and I probably would of said no difference, what a waist of time and money .

 

[Ggmac]

Now engraving is something I experimented with and can say I have with my rifles never seen any change with just a 0.001 + or - change of engraving. now speaking in reference to Lapua ammo, I have measured as much as a 0.035 difference in bullet OAL as measured from the Ogive/first driving band in some of the lots I have and they still shoot equally as well between rifles. but I am using the Nevius chamber so this may be why.
correct me if I am wrong, but HS on a rimfire is taken from between the bolt face and rear of the shell casing or back facing of the rim.
so help me understand, how changing the HS will change engraving since once the front part of the rim is seated against the breech face it can not go any further in?
firing pin indentation can be altered with HS changes.

Lee

The case isnt in complete contact with the chamber , it tilts , ever so slightly, the more headspace and with min engraving the more it tilts .
Cut a barrel chamber in half , mill away half is easier , take your ammo , place and visualize what Im trying to say , now take a fired case , from this chamber or same and see how it now is straight , base is also 90 deg which it
probably wasn’t before . Measure a fired case at rim , base and mouth , of course its almost your chamber dimensions ( almost because of springback ) subtract the measured unfired case , subtract and dang , lost my train of thought . Anyway saying the cartridge tilts is an extreme but seeing the fired case versus the unfired case shows you how much room there is in the chamber and having a tight bolt fit has shown improvement. All this is from exhaustive testing.
if Tony K Harper tested the way I did than all I can say is that its normal to have different data as theres so many other variables. Cleaning , firing pin location, extractor number and location, and this may ALL boil down to the headspace is just changing barrel harmonics. After all it is pushing harder on the breech which could change harmonics . Dang more testing.
A hypothetical, what if you were only engraving the bullet by .0005 1/2 of thousands, then your bolt is pushing the case another .001 . Wouldnt that make the bullet engrave more . Again , this is only if your ammo is say .42 rim and your headspace is set .43

 

[Ggmac]

Interesting, I would think if adjusting the HS on a H&R M12 improves the accuracy, it would work for any other rifle and not just the M12. also I am puzzled by the accuracy improvement would only be noticeable at distances beyond 50 yards I assume you meant.
it is the exact opposite of what I have seen and experience, outstanding accuracy at 50-yards generally extends to 100 yards. can't say about anything farther out as I don't shoot past 100 yards.
here is an example-
50-yds. 10-shot group and 100-yds. 3-shot group

Lee

Your 100 yd group ( if the 3 shot group) is not enough shots to get any significant data . 10 shot or 20 shot groups repeated 5 times . Then your data will be relevant. My 20 shot g
may I suggest that we take this to a separate post , we’ve gotten the original post off track .
I didnt say it wasn’t improved at 50 , it was much more difficult to measure the small improvement , by going to 100 and further you can get better data , easier to measure due to the group getting larger
Your assumption about good at 50 good at 100 is just with your ammo , gun on that day . For instance, take a high vel ammo , great at 50 crappy at 100 , going transonic. Or a border line std vel ammo thats shooting faster than it usually does , due to weather , bore , barrel length etc, doing the same thing , going transonic before the 100 yd mark .
one test with one ammo with small lots isnt good data

 

[Tony K Harper]

Ggmac,

I'm not sure what you are saying.

It is for sure I can't measure .0005 1/2 of thousands.

If you are shooting rimfire, that is a good thing.

Good luck with your testing/shooting, hope to see you at a match sometime.

TKH