Distance to Lands has increased 0.045"?

[Papa Charlie]

Tonight I was measuring my rifles distance to the lands using my Hornady comparitor to develop a load the Berger 200.20X and the Berger 215 Hybrids that I want to shoot at 1000 yards.

I have been shooting the Berger 185 Juggernauts exclusively through the barrel with my Berger up till now, so I thought I would double check my barrels wear so I measured it with my Jugs as well.

The barrel is a Benchmark 30", .308, 1:10 twist, 5R, SS, Reamer was a SAAMI National Match with a 0110" Freebore. I have been firing Juggernauts with 42.9gr of Varget that measured 2731 FPS on the 200th round through the barrel. At that time the measurement was 2.253" Base to Ogive and I have been loading for a 0.010" jump since. I had checked it around round 350-400 and everything seemed fine.

So tonight I am measuring and it would appear after 935 rounds total, the throat has opened up 0.045" more than it was at round 200. Thing is that the rifle has been shooting great. Thought it was from me getting better with my mechanics as I have only been in this game for 1.5 seasons, now I am starting to wonder if it was me or the Juggernauts wanted a bigger jump 0.055".

Is this normal wear? I am inclined to continue to load the Juggernauts for a 0.055" jump as I have been pulling 197 and 199 scores at 500 yards pretty regularly.

Second question is, I had planned to develop the loads for the 200 and 215s at 0.015" OTL, it is my understanding that they perform better with less jump. For those that have experience with these rounds, what is your experience?

Not sure if it matters, but all I use for brass is Lapua Winchester large primers. Although I plan to use the Lapua Winchester Palma's for the 200 and 215 grain Bergers.

 

[Dusty Stevens]

I wouldnt be alarmed. Just lengthen your bullets accordingly. Id check every few hundred rounds at the most

 

[Drop Port]

Did you save and use the same bullet to check it?

 

[Papa Charlie]

I wouldnt be alarmed. Just lengthen your bullets accordingly. Id check every few hundred rounds at the most

I am not alarmed so much as amazed at how much the throat has eroded over what seems like a short time. This is my first custom barrel so it may be normal. I am however, wondering now if the increased jump has improved the performance or my work on improving my mechanics and consistency or both.

I now plan to play with my Jug loads to see if there is a difference between a 0.055" jump and a 0.010" jump. Unfortunately, I don't have a 500 yard range available till March. So will have to play with the 200 yard for now.

 

[Dusty Stevens]

Tuning is a never ending process. Dont think that you can shoot the same load for even 300rds

 

[Medic505]

Look at the bright side. If you started with a 0.110 freebore and you now have a 0.155, that's just about right for the 200-20X bullet. Still short for the 215's.

On the not so bright side of things, I have never seen that much erosion in any of the .308 barrels I have shot. Even at 2500 plus rounds.

 

[Drop Port]

Look at the bright side. If you started with a 0.110 freebore and you now have a 0.155, that's just about right for the 200-20X bullet. Still short for the 215's.

On the not so bright side of things, I have never seen that much erosion in any of the .308 barrels I have shot. Even at 2500 plus rounds.

That's why I asked if it's physically the same bullet original 1st measurement was taken with not from another lot# That[s far more erosion than my 6.5x47L and I'm standing on it hard.

 

[Papa Charlie]

Actually, no I used some from a different lot. I still have some of the others and will check against some of those tomorrow. Can't believe I didn't think to check it when I saw the amount of change. Curious to see how much difference there is between the two lots. I hope a lot.
Thanks

 

[Drop Port]

Actually, no I used some from a different lot. I still have some of the others and will check against some of those tomorrow. Can't believe I didn't think to check it when I saw the amount of change. Curious to see how much difference there is between the two lots. I hope a lot.
Thanks

I made a habit of keeping the original bullet in the die box. I've checked against a strange lot I had and got an erratic reading. Curious to hear your findings.

 

[L W P]

Did you save and use the same bullet to check it?

Even if not the exact same bullet I would not think that Bergers 185 Juggernauts would vary .045" from box to box. Since the OP does say "I have been shooting the Berger 185 Juggernauts exclusively through the barrel"

 

[Ned Ludd]

If it's not the same Lot# of 185s, the difference could easily be due to Lot-to-Lot variance. I pick out 10 bullets at random from any new Lot, number them on the bottom with a Sharpie, and store them in an empty bullet box. I record the pertinent dimensional measurements of the "measurement set". I then use that particular measurement set of bullets to determine the distance to the lands regularly (every 200-300 rounds) for the duration I am loading that specific Lot of bullets. I use the average all 10 CBTO and COAL measurements at "touching" as my working values.

Dimensional variances between different Lots of the same bullet can be much larger than those within a single Lot, so I don't find your result all that surprising. This is why a load needs to be re-developed when switching Lots of bullets (or any other component, for that matter). Keeping a few bullets from each Lot for measurement purposes is a good idea and really doesn't require much extra effort or space.

Comparing the BTO from both Lots of bullets might give you the answer. However, what your really trying to do is compare the distances for the two different Lots between the point on the bullet ogive that first engages the lands and the point on the ogive where your caliper insert seats. Those two points may well not be the same. In addition, the diameters of the noses in the region just in front of the bearing surface are not the same. If you don't have the tools to easily or accurately measure bullet diameter at the exact spot that first engages the lands, and there is a discrepancy in the nose diameters based on your measurements with the same caliper insert, there is no common reference point on the bullet ogive. Just be aware that without having a single defined reference point on the ogive, you may find that simply comparing BTO measurements of the two different bullets may not fully account for the differences between you previous and current distance to touching measurements.

Nonetheless, simply repeat your distance to touching measurements with several bullets from the original Lot. The value should be much closer to the old measurement if variance in the new bullet is the culprit. In my hands, 0.308 Win loads with 185s that are very comparable to yours typically exhibit land erosion somewhere in the range of about .005" to .010" per thousand rounds fired, or about 4- to 8-fold less than the difference you measured. Your 2730 fps load with Varget and 185s is not extraordinarily hot by any standards, so I suspect you'll find a big part of the difference is the bullets. Let us know what you find. Good luck.

Edited to add: next time you have a new barrel chambered, you can ask your smith to make you a caliper insert out of the barrel stub, cutting the hole with the actual reamer used to chamber the barrel. Chances are very good it will better represent the actual chamber/throat when taking measurements than any mass-produced caliper insert you can buy.

 

[Capt. Oblivious]

I wouldnt be alarmed. Just lengthen your bullets accordingly. Id check every few hundred rounds at the most

As Dusty said, check them every 100 and keep on top of the change and adjust our DIE according. A different Lot bullets will obviously change a couple things as well

 

[Texas10]

I suspect your measuring method is not consistent, and since you're shooting only one bullet I'd like to suggest a test to confirm your measurement.

Neck (or FL) size your Hornaday modified case and seat your Jugg to the CBTO that your measurements suggest. Screw it on the Hornaday tool and insert it in the chamber with a firm push. Then retract. If the bullet it in the lands, it'll resist being retracted. If not, it's off the lands. Be sure your chamber and throat are free of carbon for this test as it is very sensitive.

Fine tune the seating depth until you know exactly where it no longer wants to stick upon retraction, and then keep that seated round as a Standard and record the measurement in your loading notebook.

In 6 months repeat the test by using an inertia tool to move the bullet forward a bit, reseat a little longer than before and adjust until just not sticking upon withdrawal.

 

[hogpatrol]

My process, YMMV, after every session of shooting, I clean and check my distance before every reloading session, same or different box or lot. Use a dedicated bullet. Some change, some don't. If it does, I attribute it to the cartridge, choice of powder and/or the barrel metal. I'd also check all of the bullets in the same box/lot. I checked BTO of Berger 168 HVLDs in one box and found a variance as large as .010.

 

[chkunz]

Did you save and use the same bullet to check it?

This is an important point, some bullets vary by several thousandths. Also this is a difficult measurement to make accurately with most of the tools that we have to make it with. Make ten measurements and average the measurements, you may want to throw out the high and low measurements. Most folks get about 0.015 per 1000 rounds.

 

[mikecr]

If you initially found best seating off the lands (OTL), you don't have to maintain that exact relationship to hold performance. Don't worry about it.
If you change bullets, re-test for best seating with them.

 

[Papa Charlie]

Ok, I measured again, this time using the rounds from the same lot number that I had original measured with. The delta after 735 rounds is 0.016". Much better than the delta of 0.045" I got using rounds from a different lot.

I have modified my load data sheets to take measurements at the beginning and then again every 100 rounds so that I can track the wear. I will track this separately for each batch I use so that it is consistent. I also plan to set aside a couple of rounds from each batch so that each time I measure I am using the same rounds.

 

[Bbear]

If I'm reading the OP correctly, he did his initial measurements with the 185 Jugs then measured with the 200 gr and/or the 215's and found a different measurement. If you change the bullet, odds are good your measurement will change as well. Your last post showed some growth with the Jugs (.016). With the 200's and 215's, you'll most likely have a different measurement due to different bullets.
Like others have said, save a handful of bullets and check every so often to see what, if any, changes you may need to adjust for.

Then again, if I'm reading the OP incorrectly, never mind.