OAL gauge question

dakota1 · Posted: Thu Sep 20, 2007 9:56 am Post subject: OAL gauge question

I received my OAL gauge yesterday. Using the modified case I ordered with it, I checked my maximum OAL. I am loading .270 Win, 130 gr BTSP Sierra bullets. Due to the boattail design, when the bullet is pushed against the lands, it is actually pushed out of the case. I think that if the bullet was a flat base it would stay in the case.

I checked to make sure the modified case would fit, by chambering it with the bolt. I cleaned my gun before measuring. I used a light finger tap, as suggested, for the bullet seating on the lands.

Is this common, or am I doing something wrong?

Thanks.

DallanC · Site Admin Joined: Jan 18, 2005 Posts: 3572 Location: Utah

Its called "freebore", the distance from the bullet to where the lands start. Some rifles design in alot of freebore to get the bullet moving before it engages the lands, Weatherby for example is famous for this. Others like the bullet to engage quicker so the lands are cut closer to the bullet.

It can be common though for there to be alot of freebore in a factory rifle where a person might shoot various bullet types which would require more or less freebore just to fit in the bullet.

Bottom line is accuracy... I have accurate rifles with a ton of freebore and some with crappy accuracy with alot of freebore so shoot yours and find out where its at. I believe you can get a good gunsmith to remove your barrel, cut it down where it threads onto the action and "set back" the rifle X distance to give you less freebore. One of our resident experts can give you more info on that... or if its cheaper to just buy a new barrel.

-DallanC

dakota1 · Posted: Thu Sep 20, 2007 10:29 am Post subject: Re: OAL gauge question

Thanks Dallan.

It's a Remington 700 BDL rifle. I didn't realize they barreled them with that much freebore. Kind of makes a Stoney Point OAL gauge a mute point.

hunterjoe21 · Posted: Sat Sep 22, 2007 6:39 pm Post subject: Re: OAL gauge question

I wouldn't discount the use of the OAL guage. When used with a bullet comparator, it will assist in seating bullets to an accurate depth and measuring true freebore. Measuring CARTRIDGE OAL with a caliper does little to ensure a consistent seating depth. There are too many variations in bullet design, and especially with HP and SP bullets, variations from bullet-to-bullet. Measuring COMPARATOR overall length gives you an accurate and repeatable measurement, which will allow you to "tweak" the freebore until you find the distance that works in your particular firearm.

As for a bullet being too short to be seated close to the rifle's lands, it is NOT uncommon to find certain light-for-caliber bullets that don't reach the lands. I had the same issue loading 40 gr. bullets for a .22-250, and even though factory loads produced decent groups, I was never able to find the right powder/primer combo to duplicate factory performance. Once I Moved up to 50 gr. bullets, I was quickly able to solve accuracy issues, mainly by seating the 50 gr. bullets closer to the lands than the 40 gr. bullets would allow.

dakota1 · Posted: Sun Sep 23, 2007 7:41 pm Post subject: Re: OAL gauge question

I rechecked my chamber, and I must have been letting the case back out, or not inserting fully, during measurement. I have been able to repeat the measurement and have found the chamber capable of seating a 130 gr boattail againt the lands. I am not planning on doing so at this time, but it is nice to know that I now have an accurate measurement.

I do have another question. I have read that a comparator would compliment the OAL gauge, for an accurate measurement from the head to the ogive. I see that Hornady has a comparator body and inserts, which seem straight forward, and the illistration shows it being used with the OAL gauge, again straight forward. What is the Anvil base kit for? Is this to be attached to your caliper so OAL can be done with an actual loaded round? Sinclair has a comparator that looks like a hex nut. Any opinions? Likes or dislikes of either?

Is this benchrest stuff, or can a hobby shooter, with a 700 BDL actually benefit?

Thanks for any input.

Deleted_User_2665 · Super Member Joined: May 06, 2006 Posts: 380

Re: Remmy 700's less a custom barrel, ie factory.

Seat to function through the mag box....for starters, with at least a full diameter width of bullet seated in the neck.

With that variable set in stone for the time being begin load developement, adjust charge weight per OCW practices to glean The Sweet Spot.

If need be, then tweak the seating depth to shrink groups if so inclined.

Intial Sweet Spot should reveal MOA groups or less....beyond that is a bonus.

Once accomplished, a solid OCW load negates much garbage others fret much......like freebore.

THE most accurate load, consistant 1/2 MOA, in my factory .270 700 BDL was 90 grain Sierra HP's, and they jumped at least a quarter inch of freebore.

FALPhil · Posted: Mon Sep 24, 2007 8:41 am Post subject: Re: OAL gauge question

dakota1 wrote:

Kind of makes a Stoney Point OAL gauge a mute point.

It would be a moot point too. Very Happy

dakota1 · Posted: Mon Sep 24, 2007 9:00 am Post subject: Re: OAL gauge question

What is OCW?

Deleted_User_2665 · Super Member Joined: May 06, 2006 Posts: 380

Optimal Charge Weight.....

Not widely recognized by the masses and highly poo poo'd by those who thrive on frettin' voodoo, fiddle fartin' around with numerous gadgets, and insist on taking extra steps.

If you've ever wondered why some powders are temperature sensitive, why different lots of components affect a load, why some handloaders loads are successful with a certain brand of brass but fail with others, if you've ever chased the occasional flyer while scratching your head.............then you need OCW.

It makes leaps and bounds toward negating variables that affect pressure sensitivity on many levels. Pressure, by all accounts of the Laws of Physics, is the heart of the beast.

Freebore is a variable that cannot be adjusted without a smith's help, so it is a given and is constant. Aleviating the other varibles in the equation that plague a handloader makes such things as freebore less of a concern......

If you are interested in studying the OCW principles and gaining an insight on a superb method of load development I'll PM you a link to a bestest explaination of it.

guncollector · Posted: Tue Sep 25, 2007 2:10 pm Post subject: Re: OAL gauge question

I shoot that same bullet in a 270 Rem 700 and got best results 0.020 off the lands. You really do need a comparator to go along with the OAL gage especially if you are getting close to the lands. A bullet with no jump space will result in significantly higher pressures relative to one with at least a few thousandths of jump.

Generally speaking, the best accuracy will be somewhere between 0.02 and 0.06 off the lands. For some reason, Barnes bullets need more jump space - typically 0.06 to 0.08 in my experience.

Something interesting I didn't know until recently was that cast bullets almost always shoot best with no jump space. A little higher pressure with them is not an issue since they must be loaded quite mild compared to jacketed bullets.