Method for determining OAL

[.375Mojave]

I do not have any sophisticated equipment for determining how to load a round a set distance off the lands. The method I have used is to size a case mouth to have a snug slip fit on the projectile, set the round well beyond expected OAL and chamber the round. I will do this several times to get a good feel for the resistance and come up with a consistent average dimension.

I rely on the contact with the rifling to seat the bullet to depth, understanding that it is likley already into the lands a couple thou. I assume this interference and deduct maybe .002 as an assumed zero jump/in contact round.

Can anyone recommend any enhancements to this method to assure precision? I have tried blueing the bullet afterward to see if there are signs of contact on a round that should be .002 to .005 off the lands and do not see any marking from contact, but I am not really sure if this is telling me anything.

I appreciate any insights anyone has or any tricks for determining this.

FYI the current rifle in question is a 338 LM and I use a Comparator to eliminate the variability of mis-shapen or damaged projectile tips.

 

[nutzo396]

Re: Method for determining OAL

Pretty sound concept and it mimicks what I do also. I made a couple stops that slide over my cleaning rod. Close the bolt without anything in the chamber and zero the first stop on the bolt face. Then put in an unloaded round with the bullet seated long. I use a rubberband on the back of the bolt to hold the bullets against the lands while I set the second stop. Measure between the 2 stops and your done....except for having to do the same thing 5 more times to get an average.It may vary 0.005 or so.

 

[.375Mojave]

Re: Method for determining OAL

Sounds reasonable and with weight of unloaded round only it should give a good reading on contact with the lands. The force required to push the bullet in is my biggest concern about my method as I am not sure how quickly resistance builds with land contact. I am also concerned with sticking in the lands drawing the bullet back out and giving a falsely long reading.

The trick with your method seems like the stops and how accurately they can be measured. What are you using for those?

 

[nutzo396]

Re: Method for determining OAL

Just 2 pieces of 1" Diam round steel. Drilled and reamed slightly oversized so it will slide along my rod. Tapped the side of the 2 so a screw will go all the way into the center hole to tighten onto the rod.By tighten I mean barely finger tight as to not mar the rod. I woundn't worry too much about too much force. If you pull the bullet out after measuring and can see marks from the lands, you need to use a lighter touch.

 

[.375Mojave]

Re: Method for determining OAL

Thanks for the tips.

i will try to get some collars made up and compare the results of the two methods.

I will let you know how they compare.

 

[MitchAlsup]

Re: Method for determining OAL

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: .375Mojave</div><div class="ubbcode-body">I rely on the contact with the rifling to seat the bullet to depth, understanding that it is likley already into the lands a couple thou. I assume this interference and deduct maybe .002 as an assumed zero jump/in contact round. </div></div>

In order for this uncertainty NOT to get you, be sure to load the final round either a 5 thou into the lands or at least 10 thou off the lands. That is, either jump 'em of jam 'em. The 15 thou dead zone accomodates all dimensional changes due to temperature without nasty surprises.

 

[Bob 964]

Re: Method for determining OAL

This link may help. Removing the firing pen will minimize resistance when you re-insert the bolt.

http://www.youtube.com/watch?v=Jv-D1mEI514&feature=related

 

[.375Mojave]

Re: Method for determining OAL

In your experience, have you seen better results on average by jamming them over jumping them?

If accuracy improved at the expense of a few FPS it might be a trade I would make in my hunting rifle. I am not trying to push the outer limits of supersonic flight as this round of questions is aimed at my 338 LM. This is a hunting rifle for me and it is highly unlikley I would try to use it beyond 1,200 yards, well within the supersonic range regardless of a minor MV reduction.

 

[MitchAlsup]

Re: Method for determining OAL

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: .375Mojave</div><div class="ubbcode-body">In your experience, have you seen better results on average by jamming them over jumping them?</div></div>

I have been a jumper over my reloading career.

My typical long range loading get one 0.35" 5 shot group, two 0.5" 5-shot groups and one 0.6" 5-shot groups from a box of 20.

The gun has a factory barrel, chamber, and long throat--so it is not clear if jamming would improve things. But what is clear is that what has been developed shoots quite nicely.

 

[HPLLC]

Re: Method for determining OAL

Sinclair bullet comparator

Apparently Sinclair makes some tools that are designed to assist in determining OAL as it concerns where the bullet will address the rifling. It appears that this will allow you to determine whether the round is the right length, after you know what length to the throat is.

 

[TexIndian]

Re: Method for determining OAL

This is covered in detail in TresMons' sticky articles at the top of this section - the one about finding OAL.

Back before I became a fancy tool junky, I used a Dremel tool to cut a slit into the neck of a case. Then I did essentially what the OP describes to find where I first contacted the lands.

 

[.375Mojave]

Re: Method for determining OAL

I have a Sinclair Comparator and it is what I use to check loaded rounds. That tells you what the loaded round measures using the Comparator, but does not tell you what your chamber is reamed to.

I have a tight necked 375 CT Improved (my own design and reamers from Dave Kiff at Pacific Tool) that I can fire form brass and give me a nice slip fit on a bullet.

That is what I chamber and measure to try to determine an OAL for a bullet in contact with the lands as described above, but I can do it 10 times and come up with small variations (.001 to .003) in OAL and every now and then get one that reads way long (.020 to .030) but believe this is the result of the bullet lodging in the lands and being withdrawn from the case.

I was looking for some feedback on the way other guys do it and my new Savage 338 LM is a factory chamber I am reloading for the first time, so I am back to my method to determine OAL.

I will probably try the slit neck technique if my expander button gives me too tight or loose a fit. I think I am going to shoot for .010 of jump and develop from there. If i can't get any good loads I will tinker with less or more freebore.

I appreciate the input.

 

[Clark]

Re: Method for determining OAL

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: .375Mojave</div><div class="ubbcode-body">In your experience, have you seen better results on average by jamming them over jumping them?</div></div>
I jam bottle neck cartridges into the lands half way between touching and getting stuck... magazine length and neck length permitting.
This is the most accurate for me.

I roll crimp straight wall rifle cartridges into the canalure in 44 mag and 45 Colt.
This is the most accurate for me.

 

[.375Mojave]

Re: Method for determining OAL

Appreciate the feedback. What rifle rounds are you loading jammed?