2 distinct resistance points when measuring Maximum OAL for 308

B

bajadiver

Guest
Hello everyone, I'm relatively new to reloading, and your suggestions are greatly appreciated.

I'm using the Hornady OAL Gauge for my Ruger M77 VLE in 308 and I have some doubts about where the rifling actually begins. I understand it's all about relative consistency, but generally speaking, where to take the measurement?

When gently pushing the bullet through the gauge, I encounter two distinct resistance points. The first one is obvious and the bullet stops, but if I push a little harder, the bullet pushes past it, about .10 in, then completely stops and won't go further, no matter how hard i jam.

I did this same operation probably 20-30 times and always encounter the two resistance points.

At the first resistance point, I do not need my cleaning rod to push the bullet out, it will fall out easy.

At the second resistance point, I definitely need to push out the bullet out with the cleaning rod..

When I examine the bullet, I can see very slight parallel scratches( about .10 in long ), which I assume are the riffling. These are not deep grooves because it still feels smooth to the touch, but does catch my nail ever so slightly.

So for measuring max oal, is it common practice to push the bullet into the rifling for the measurement until it stops? I'm assuming this is why I get the scratch marks.

Or should I measure up until it just touches, making no marks? I'm assuming this is the first resistance point. This is a funny place for me to measure because it's not consistent. The second resistance point gives me a fairly consistent measurement.

My understanding is that you need "some" jump lest your pressure might be to high. Does seating the bullet at the first resistance point technically allow for jump? I cant imagine that the little extra pressure I applied to get to the final resistance point will effect the internal pressure of the powder when firing.

How far off am I in my assumptions.

Thanks for your input.
 
You may have a buildup of carbon in the freebore area of your barrel's throat that is causing you to have to apply extra pressure to put the bullet where it finally stops.
 
baja my man, welcome to the rest of your life....... WHY!!!

:)


It's good to see you asking questions.

I'll share my opinions on them, hopefully point-by-point;



I'm using the Hornady OAL Gauge for my Ruger M77 VLE in 308 and I have some doubts about where the rifling actually begins. I understand it's all about relative consistency, but generally speaking, where to take the measurement?

When gently pushing the bullet through the gauge, I encounter two distinct resistance points. The first one is obvious and the bullet stops, but if I push a little harder, the bullet pushes past it, about .10 in, then completely stops and won't go further, no matter how hard i jam.

I did this same operation probably 20-30 times and always encounter the two resistance points.

At the first resistance point, I do not need my cleaning rod to push the bullet out, it will fall out easy.

At the second resistance point, I definitely need to push out the bullet out with the cleaning rod..
Click to expand...


Somehow your setup has 2 resistance points and as you appreciate, the first one is unreliable. I suggest you ignore it. As to WHY it's there, I dunno. I would figure it out if I had it in my hand, my guess is burrs from the reamer, but at this point, I dunno...... so my advice is to ignore it. :) It's of no use to you. As you've surmised, you need a solid, repeatable place from which to take your measurements, and your notes. At any rate, THIS pertickler bullet is finding some resistance prior to what could be termed "full jam," that point at which it will be pushed back into the case before it goes further into the lands.

So use it.


So for measuring max oal, is it common practice to push the bullet into the rifling for the measurement until it stops? I'm assuming this is why I get the scratch marks.
Click to expand...

In your case I'd use the "deep" setting, the repeatable one, the one with .010 long scratches, remember no measurement of "oal" is useful without the measure be taken from the ogive surface near to the point at which it engages the rifling lands. No, your situation isn't common, I've never seen it, but it is what it is, go with it....


My understanding is that you need "some" jump lest your pressure might be to high. Does seating the bullet at the first resistance point technically allow for jump? I cant imagine that the little extra pressure I applied to get to the final resistance point will effect the internal pressure of the powder when firing.
Click to expand...

This one kinda' pi$$es me off...... I know, I know, it's right from the reloading manuals. They all talk about how "your pressure will skyrocket if you so much as TOUCH those wickid lands.." First let me assure you, DON'T FEAR THE LANDS!!! You're not gonna' get in trouble here..... In fact I know of many rifles where the pressures actually DROP with firm land engagement..... but please test this for yourself. Use a chronograph, it's a hunnerd dollars well spent. A chrony will save you many times what it costs and best of all it makes you SAFER which is a big deal to me. And it will shorten your learning curve immensely.

Ask lots of questions, questions beget questions. The only stupid question is the one you didn't ask.
Take lots of notes, learn NOW to take the time. It'll save time and money and make you 100Xmorebetterfaster
Be honest with yourself. You can lie to your buddies all day but for pete's sake COUNT EVERY SHOT for yourself :)

I hope this is helpful
al
 
My two cents worth

If you have access to a bore scope with a sufficient length probe you will be able to insert it from the muzzle end and see what the first resistance point is. My guess is a ring of carbon. The second resistance point is where the bullet contacts the lands. You can get more than just land contact if you start pushing. The engraving marks on the bullet will become more square as the contact increases. However I hope you are doing this OAL test with a case that has been fire formed in that barrel. Otherwise the difference in measurements can vary quite a lot.
Andy
 
thanks

Thanks Boyd, Al and Andy,

Al, I know, I know....why?? Because I don't golf!! lol!

Everything you guys said makes sense. I started shopping around for a borescope to see what's causing the first resistance....they sure ain't cheap. Carbon ring makes sense. I may just go to a gunsmith and have them take a look. Hopefully, just needs a little more cleaning. On the other hand, that snug carbon ring might just make the bullet jump into the lands straighter? I'll experiment.

Thanks guys

Javier
 
I don't know of any bore scopes that are long enough to see a carbon ring in the throat when inserted from the muzzle, but you should have no trouble working from the other end. One more thing that can cause what you are feeling is a ridge of metal right at the front of the chamber neck that was pushed up by a dull reamer that was pushed pretty hard during chambering. I have seen this from another cause ( I think) but I believe that Gordy Gritters mentioned this on another thread which was (again, I think) about lapping chambered barrels. The one that I had was fixed by running in a throating reamer, with a close fitting pilot, very carefully, by hand. We were not guessing about what it was. My friend, who fixed it for me, and I both had seen it with a bore scope. If you know someone who has one, they can be very handy for diagnosing this sort of thing. My little problem could not be seen by looking down the barrel, even with it off of the receiver.
 
bajadiver said:
When gently pushing the bullet through the gauge, I encounter two distinct resistance points. The first one is obvious and the bullet stops, but if I push a little harder, the bullet pushes past it, about .10 in, then completely stops and won't go further, no matter how hard i jam.

When I examine the bullet, I can see very slight parallel scratches( about .10 in long ), which I assume are the riffling. These are not deep grooves because it still feels smooth to the touch, but does catch my nail ever so slightly.
Click to expand...

It's no coincidence that the scratches are the same length as the distance between the resistance points. At the first point, you have just touched the bullet to the lands. No scratches yet. At the second, you have forced the bullet into the lands as far as the force you applied allows, which is 0.1 in past touching. Thus 0.1 in scratches. For a 1.5 degree lead angle, this corresponds to deformation of the original touching points on the bullet of about 0.003 in, which should just catch a nail. This is consistent with your observations.

The trouble with seating depths is that there aren't reference points that are easily measured. It is easy to deform a copper/lead bullet a few thousandths (like to your second resistance point). If you pushed progressively harder (with some mechanical advantage, obviously), the bullet goes deeper and deeper until eventually you push the bullet all the way through the bore. So the measurement you get depends on how hard you push. With a very hard bullet (diamond?), it would be easier to indicate the touching point, although the steel lands can still deform.

The good news is that you don't really need to know with a lot of accuracy how far the bullet is jambed to load accurate ammo. You only need to make sure the base-to-ogive length of the loaded rounds are consistent at whatever dimension shoots best. It is good to know the jamb length, by whatever measurement method you choose, so that you can adjust for throat erosion, but it otherwise doesn't matter.

Cheers,
Keith
 
Keith,

With all due respect, I don not believe that one can push a bullet .100 into the lands with finger pressure using one of these gauges. I have one. One of the things that friends that have carbon problems in their rifle's throats have seen is scratches on the bullet of a loaded round that has been chambered and then removed from the rifle. These show up after a number of rounds are fired after a proper cleaning, when firing a powder that is prone to this sort of problem. Changing powders has solved this particular problem. The scratches did not show when the same thing was done with a clean barrel. Although I have always thought that VV powders would be uniformly clean, this showed up in a couple of varmint calibers (.204 & ...22-250) with VV140.

Boyd
 
Bore scopes aint borescopes

Boyd Allen said:
I don't know of any bore scopes that are long enough to see a carbon ring in the throat when inserted from the muzzle, but you should have no trouble working from the other end. One more thing that can cause what you are feeling is a ridge of metal right at the front of the chamber neck that was pushed up by a dull reamer that was pushed pretty hard during chambering. I have seen this from another cause ( I think) but I believe that Gordy Gritters mentioned this on another thread which was (again, I think) about lapping chambered barrels. The one that I had was fixed by running in a throating reamer, with a close fitting pilot, very carefully, by hand. We were not guessing about what it was. My friend, who fixed it for me, and I both had seen it with a bore scope. If you know someone who has one, they can be very handy for diagnosing this sort of thing. My little problem could not be seen by looking down the barrel, even with it off of the receiver.
Click to expand...

Most shooters use those hawkeye units. Mainly because they are cheap compared with other types. I have a zeiss surgical scope that came with several length rigid tubes with 90 degree prisms and a flexible fibre optic type. No trouble seeing into the chamber from the muzzle. If the resistance is from a carbon ring then a quick wipe with CTC or equivalent compound will remove it easily. If the barrel is a factory job then the above mentioned metal ridge from a dull reamer is also quite likely.
Andy.
 
Boyd Allen said:
Keith,

With all due respect, I don not believe that one can push a bullet .100 into the lands with finger pressure using one of these gauges. I have one. One of the things that friends that have carbon problems in their rifle's throats have seen is scratches on the bullet of a loaded round that has been chambered and then removed from the rifle. These show up after a number of rounds are fired after a proper cleaning, when firing a powder that is prone to this sort of problem. Changing powders has solved this particular problem. The scratches did not show when the same thing was done with a clean barrel. Although I have always thought that VV powders would be uniformly clean, this showed up in a couple of varmint calibers (.204 & ...22-250) with VV140.

Boyd
Click to expand...

If the pattern of scratches matches the lands, the source is pretty clear. Otherwise, you are probably right.
 
When trying to see the marks on the bullet to determine where or when it touches the lands it is helpful to do this:

Seat the bullet in an empty piece of brass. Take some 0000 steel wool and twist the bullet in it until the bullet is well burnished by the 0000 steel wool.

The marks or scratches will show up much better. Use a good loup.

I don't use that tool for pushing the bullet. I seat the bullet a little long and chamber using the bolt. This way I get good marks. I then start adjusting my seating die to what ever or where ever I want and check again.

Remember it is only a starting point from YOUR measurement. I have started with square marks on a couple of .308's with cup and core bullets. With solids such as Barnes 0.050 off or more.

Good accuracy can depend on seating depth.

A micrometer seating die is very helpful.
 
bajadiver said:
Thanks Boyd, Al and Andy,

Al, I know, I know....why?? Because I don't golf!! lol!

Javier
Click to expand...

Javier,

I do play golf. Rifles, as fickle as they sometimes can be, are a lot less frusturating than golf. Plus you don't have to wear one of those stupid white belts and ridiculous plaid pants when shooting.

I'm leaning towards a bit of carbon causing your first resistance point. I would think that a typical, long throated factory chamber would give carbon a big canvas on which to paint on. It's gotta go somewheres...and the throat is the first thing it's gonna see.

I would wrap a patch around a 308 caliber NYLON bore brush, smear a bit of JB Bore Paste on it, and short stroke the throat area 20 or so times (use a bore guide!), followed by a thorough cleaning. Then re-check your seating depth to see if that first resistance point is still there.

After reading about Gordy Gritters and Dave Tooley polishing throats, I did the above on a just-chambered Lilja 3 groove. Through my bore scope, the before and after was quite noticeable. It was less...I don't know...I guess "scratchy" looking afterwards. Maybe "softer" is a better description.

I agree with ol' Alinwa about the not fearing the lands. When I'm working with a new rifle, I always start INTO the lands about .005-.010, and work up from there. As Al pointed out, most loading manuals state that is where your pressure will be the highest. So if I'm safe there, I feel pretty warm and fuzzy bout' things if I reach a max load and decrease OAL to the ojive from there. Additionaly, if you start at or into the lands, it leaves you with only one direction to go when fine-tuning seating depth for accuracy: Backwards. To me, it's a lot easier than starting .020 off the lands, and then chasing your tail going longer and shorter.

Of course, Alinwa has got me thinking about his higher chamber pressures at a shorter OAL comment. I always believed the reloading manuals and assumed...

...maybe I'll go dust off my old Ben Hogan's and hit the links. My head hurts.

Hope it helps,
Justin
 
Agree with the above and... If you wrap a brush with a patch (wrapping the patch around the brush like it was a Parker Hale jag) so that the patch is just a little past the end of the brush, and the whole thing is a snug fit in the neck of the chamber, and put it on a chamber rod, you can shove it in till you feel a definite point of resistance , and you will be at the end of the neck, at that point, with some JB on the patch (I work it into an oiled patch between thumb ind finger.) if you twist it several turns, you will be cleaning the neck, the dirty little corner at the end of the neck, and the angle to the freebore. I think that this variation may clean the corner better. The trick is getting the diameter of the brush and patch right.
 
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