I could use some help making sense of the overall length findings from this rifle...
This weekend, I finally got a new rifle for my coyote friends. I want to exclude the name brand for now, just so I can get information based on facts and not based on brand preferences. However, it is important to add that the rifle is bolt action and chambered in 22-250.
When I got it home and started to get some data together for my reloading I came up with some strange findings about the chamber's overall length.
Firstly, let me add that my "overall length gague" is a re sized and de-primed case that has had the primer pocket drilled and tapped to accept a small bolt. This allows me to start a bullet into the case throat, measure, chamber it into the rifle with the bolt closed and then measure again, each time using my Hornady bullet comparator. This second measurement indicates the overall length of the round when the bullet is "jammed" into touching the riffling. I have used this method with a couple of different rifles with good results..... until now.
I always make a written note of the overall length both before and after chambering the round. My notes indicate length measurements varying a great deal more than I have ever noted before. While I do not have those notes in front of me right now, I seem to recall the difference in length measurements being as much as .015 variance!
Closing the bolt very softly or "slamming it home" does not seem to be the determining factor. I have double checked the results and still come up with very widely varying overall lengths.
So my question to our learned and experienced readership is this: Why such a wide variation in measurements? I know my method is sound, as I have had success using this described method several times in the past. But I am having doubts in this case.
I know that there is no way to accurately seat my bullets to a certain amount of jump to the riffling without knowing this crucial maximum measurement. And I know that having the correct "jump to the riffling" is an integral part of accuracy.
Could the rifle have a strangely messed up chamber or throat? Is there a problem with the riffling in the barrel? ( I tend to doubt problems in the rifle itself, as I shot this rifle this weekend and was very pleased with the accuracy and especially the groups it produced)
I would appreciate any thoughts here.... Thank you all.

Could be your bullets are being pulled out slightly when you withdraw the dummy round from the chamber. Try marking your bullets with a black magic marker first then look for evidence of the bullet being pulled out from the case mouth.

quote:

I seem to recall the difference in length measurements being as much as .015 variance!

Like many others, you're over-thinking the issue. There is little, if any, value in knowing specifically what the OAL that will allow for max length to the lands because it rarely helps accuracy and seating at the lands ALWAYS increases both powder burn rate and peak pressure.

Most factory rifles and common bullets shoot their best when loaded from 20 thou off the lands to as much as 5x that much. Thus, all we really need to know about bullet/lands contact is an approximation that's sufficently close to provide a rational reference point for seating tests when we start load development. After finding the best shooting powder/charge then work deeper in maybe 5 thou steps until you find the best seating depth.

IF you work carefully and keep records, you're probably going to find a range of both powder charge (+/- .2gr.) and seating (+/- 5 thou) in which such tiny differences make no difference in practical accuracy; then load in the middle of each range so small variations won't cause mysterious 'fliers.' Anyone who has a quirky reload that sees the effect of .1 gr of powder or .001" of OAL variation that blows his groups has not chosen his load very well.

quote:

Originally posted by Jim C. <><:

quote:

I seem to recall the difference in length measurements being as much as .015 variance!

Like many others, you're over-thinking the issue. There is little, if any, value in knowing specifically what the OAL that will allow for max length to the lands because it rarely helps accuracy and seating at the lands ALWAYS increases both powder burn rate and peak pressure.

Most factory rifles and common bullets shoot their best when loaded from 20 thou off the lands to as much as 5x that much. Thus, all we really need to know about bullet/lands contact is an approximation that's sufficently close to provide a rational reference point for seating tests when we start load development. After finding the best shooting powder/charge then work deeper in maybe 5 thou steps until you find the best seating depth.

IF you work carefully and keep records, you're probably going to find a range of both powder charge (+/- .2gr.) and seating (+/- 5 thou) in which such tiny differences make no difference in practical accuracy; then load in the middle of each range so small variations won't cause mysterious 'fliers.' Anyone who has a quirky reload that sees the effect of .1 gr of powder or .001" of OAL variation that blows his groups has not chosen his load very well.

Thats funny because I shoot Bench Rest Hunter Class and always get my best accuracy by seating right tight to the lands.Every Rifle and bullet have different likes and dislikes.Some like to be seated as close as possible to the lands and some 50 thousands off the lands.To come up with 20 thousands and say thats the magic number for all Rifles makes me think you have not much experience in the Shooting Sports.

It seems to me you got two different sports goin on. Ive got a benchrest rifle I seat on the lands but I dont want to have to jam myhunting rifles so I back them off a little. Ive got a TC encore you cant find the lands in. I kept seating the bullet out farther until I was ashamed of myself and never did find em. The lawyers do want you seating on the lands.You might run the pressure up and blow one up. Then you could put the blame on tc. Ill get off my soapbox.

I would look for Labman's answer first. Then I would go about it in possibly a slightly different fashion. I would seat the bullet to a known length, shoot, record accuracy and any indication of pressure. Lengthen (or shorten depending on where you started) a slight measureable amount and repeat. When you get what shoots best according to your standards, then call that length your "go to" length and be done with it.

I have a 264WM that likes the bullets seated into the lands to the point that I seat the bullet somewhat long and chamber the round and extract, and I am done. It doesn't matter what bullet, it just likes them this way. I went through your process for a long time before I figured this one out. BTW, I do not load it to max loads either, because I do understand the lands and max loads do not play well together usually. Shoots 1/2" groups IF I do my part right with both the 125 Partition and 129 Hornady. And to the same point of impact.

"Thats funny because I shoot Bench Rest Hunter Class and always get my best accuracy by seating right tight to the lands....To come up with 20 thousands and say thats the magic number for all Rifles makes me think you have not much experience in the Shooting Sports."

If your specious response is an accurate indication of what you got out of my post it makes me think you need more experience in reading comprehension.

quote:

Originally posted by Jim C. <><:
"Thats funny because I shoot Bench Rest Hunter Class and always get my best accuracy by seating right tight to the lands....To come up with 20 thousands and say thats the magic number for all Rifles makes me think you have not much experience in the Shooting Sports."

If your specious response is an accurate indication of what you got out of my post it makes me think you need more experience in reading comprehension.

Pretty hard to get past this statement.
"Most factory rifles and common bullets shoot their best when loaded from 20 thou off the lands to as much as 5x that much."

quote:

Originally posted by blackface:
It seems to me you got two different sports goin on. Ive got a benchrest rifle I seat on the lands but I dont want to have to jam myhunting rifles so I back them off a little. Ive got a TC encore you cant find the lands in. I kept seating the bullet out farther until I was ashamed of myself and never did find em. The lawyers do want you seating on the lands.You might run the pressure up and blow one up. Then you could put the blame on tc. Ill get off my soapbox.

Nope,I do it on my Hunting Rifles also.I do not put a round in the chamber until I am ready to shoot.Just like any other Safety Concious Hunter would do.

I'm not an "F class" shooter,but I have reloaded for 20 + years ....

COAL,will vary ,the bullet manufactures know this ....

The "Ogive" should always be the same in the bullet manufacturing process ....so each one seats correctly/the same...Measuring COAL,is fine for feeding from a magizine,but not in backing the bullet off of the lands ....

Measure each case and bullet carefully and you'll se the difference ....finding 10 identical empty cartridges that are the same length and weight will be difficult....

My 2 cents ,

Jim

Nothing's certain to start with, that's the only predictable issue. Each rifle has its own preference regarding ogive to lands position. Despite using a Stoney Point OAL gauge, I still have to content myself with an average OAL value, derived from several measurements. I never met a bullet box where all bullets were 100% identical in terms of length or ogive profile...

quote:

I never met a bullet box where all bullets were 100% identical in terms of length or ogive profile...

I will concede to that if you can measure differences up to 0.005mm.

Some pretty good thoughts here and I appreciate the time each and everyone has taken to chime in and offer their thoughts. I would rather that this did not turn into some big debate where two otherwise perfectly behaved gentlemen turn into arch enemies! I mean c' mon guys, it's not that big a deal!

I think that perhaps the number one thing I have taken from these posts thus far is that I am likely just trying too hard!
I think I will make an attempt at the method described where I can choose a particular length and then increase or decrease that length and carefully watch what the groups do. AFTER seeing if the dummy bullets are being pulled slightly out of the dummy cases. I can see where that is a distinct possibility.
I have not given up on this rifle, I like it too much, and I am sure that we can eventually find a load that outperforms the factory stuff and brings the best out that the rifle has to offer. For me, that's what reloading is all about.
So you fellow's quit arguing!

You said: "Pretty hard to get past this statement.
I said: "Most factory rifles and common bullets shoot their best when loaded from 20 thou off the lands to as much as 5x that much."

It's quite difficult to see how you could read a suggested range of 20 to 100 thou of jump for most factory rifles as a fixed 20 thou for anything and that makes it hard to miss that you are having trouble comprehending what I did say.


You said: "To come up with 20 thousands and say thats the magic number for all Rifles ..."

I clearly didn't suggest a "magic" 20 thou off for any rifle but maybe your perception depends on how YOU read it! ??

And, giving us your example of your custom target rifle and bullets as if it's typical of factory rifles and common bullets suggests you don't yet have the experience to understand there are some significant differences between those two classes of rifles.



-----------------------------------

Jaybald, you do have the point of the OAL/jump stuff. Sorry, but this pompous web guru/expert stuff is just too amusing to ignore but I'll stop now.