Big Change in Seating Depth.

[Bigwheels]

I have been loading my 300 WM with 220gr.Sierra MatchKings for a couple years now,& Hadn't thought too much about how much bullet was inside the case 'till now.I have changed my seating depth .210" longer.I was seating them to the SAMMI Max OAL of 3.340".Now they are @ 3.550".This is within the 15-30 thousandths recomended by the Nosler #5 book.For free clearance to the rifleing.My question is.Will this change my MV. with the same powder charge?Thanks.

 

[remingtonman_25_06]

It sure will. You will notice a bit of increse in velocity. This is due to the longer OAL and your bullets closer to the lands which means theres more pressure which means theres more velocity. I've run simple tests on my .222 and with the same bullet/powder/case/primer components, if you change even the OAL .010" it changed the velocity about 10-20fps.

 

[Guest]

I can't argue with Remingtonman's tests, but I can tell you that, generally speaking, you might notice a bit of a fall off in MV, too, based on increased case capacity making the round generate less overall pressure. It remains to be seen how much your velocity changes and in which direction, based on the loss of pressure from case capacity increasing and the increase in pressure due to seating closer to the lands. Keep us posted, and we can find the definitive answer for your rifle, at least. I am curious. May have to start playing with seating length just to see what happens.

 

[Bigwheels]

Thanks for the input guys.I knocked the bullets out enough to reseat them to the new OAL in the ones I had left over from the last match,& I'll test them out when I have the weather to run my chrony.(May be a while.)& then we'll all know.I hope it actually stays the same,so I don't have to either re-work my load &/or re-work all my ballistics.Either would be a real pain this time of year.

 

[rick smith]

You will not see enough change to cause a change in your ballistics. Pressure doesn't start to increase until you engauge the lands.Rick.

 

[Ol` Joe]

I doubt you`ll see any notable difference. I work up my loads with the bullet touching the lands and back off after I find my max load that appears most accurate in 0.005" increments.
In the 6.5x284 with H4831 under a 129 gr hornady SST I recorded the following;
COL - 3.160" vel = 2736 fps for 5 rds
COL - 3.165" vel = 2751 fps
COL - 3.170" vel = 2749 fps

The 260 Rem, 120gr Sierra SP- R19 ( COL are total measurment of stoney point comparator and cartridge)
COL - 3.250" = 2782 fps for 5 rds
COL - 3.260" = 2797 fps
COL - 3.270" = 2794 fps

In both cases the longer COL had the bullet touching the leade. The velocitys were for 5 rds and the averages of each fell pretty much within the extreem spread of the load. All were shot on the same day, with same lot # components, loaded at the same time. I have done others with up to 0.050" variation and the result was similar. The velocity spread doesn`t mean there is no pressure difference, just that it doesn`t show as an increase in speed if it exists. I now have a Pressure trace and should one day run some comparisions with it to see if I can find any variation in pressure with COL change.

 

[Bigwheels]

Thanks.I'm not really concerned about pressures for this load.It's for competition only,& @ 1/2gr above the starting load.When I was shooting casually with the bullet seated to the SAMMI OAL.I was still able to group verry tight.Like 1.5" @ 500yds.But I would occasionaly have a "flyer".I assumed that I must have been flinching or something.But when I started to compete,I was finally able to have someone watch the rounds fly in a scope,& the ones that "flew" on me were "wobbley" :? :grin: .I finally realized that it must be something to do with my handloads.Did some research,& found I was seating my bullets way too deep.I have now corrected this,& need to re-check everything before my next competition.I just hope they stay the same,except for the "flyers".Thanks,I'll let you know what happens when I can get my chrony out.

 

[rick smith]

Bigwheels, you also would do well to check concentricity of the loaded bullet. It is not always how far you are from the lands, the bullet needs to be concentric. You need to chronograph your shot strings and check the velocity of those fliers. I load for a couple competitive shooters so am familiar with your problem. Once you get past 300yards, loading is more demanding than hunting loads for up to 300yards.
Stan Watson has written a manual based on the 30/06 where he tested various combinations both with a pressure gauge and chronograph. Different brass, bullets, primers, seating depth, etc. while other components were held constant. Excellent reading and sheads light on many misconceptions.Rick.

 

[big rifle man]

bigwheels, I've had the opportunity to try both through my chronograph and found that when increasing the OAL pressures go down and therefore velocity goes down. If you move the OAL enough to have the bullet touch the rifling then pressures go up and velocity also.

 

[Bigwheels]

Thanks guys.I really appreciate the info.I may be able to chrony these rounds this weekend,but I'm not holding my breath.After thinking it over for the last few days,I believe I'm going to have to increase my powder charge to get my velosity back.I moved the bullets out nearly 1/4",so there is a LOT more volume in the cases now.& my "Flyers",I think are a result of the bullet entering the rifleing at an odd angle,because the base of the bullets were WAY too far inside the case.This may cause the bullets base to drop down when the case neck expands to seal the chamber.I may be totally off in this,but I guess,I'll see.

 

[Guest]

I doubt the bullet is dropping down when the case expands, just because the case expands as it pushes the bullet out. The neck area still holding the bullet is not going to experience gas pressure because the bullet is 'blocking' it, so to speak. Now, there are several possibilities for the fliers. Excessive freebore can cause it, because the bullet can jostle around a tad and enter slightly off, which can be a flier at distance. This is what you meant when you talked about the bullet dropping, I think. Anyway, You could be getting fliers based on runout, as someone else mentioned prior to my posting. Or you could just have a few bullets a little off from the rest in terms of weight, jacket uniformity, or some such. I doubt that last one is the cause, but there's a slim chance it could be. Or it could be certain pieces of your brass are a little off of square, which could cause the fliers. You might try marking the brass and see if it is always the same cases. Wouldn't have to mark but four or five to test it, either. If they all fly straight, not the brass, if they all scatter, could be the brass. Keep us posted.

 

[Bigwheels]

Yes.I think my flyers are from the bullets entering the rifleing funny.due to excessive frebore,etc.I'm planing on getting the tools needed to check runout.I don't know about the brass.I use allmost all Winchester brass.But a few of them are Federals.One of the flyers was from a fed. brass.Not sure about the rest.I'll try to check on that.Theres another storm moveing in tonight.Should blow real good tonight.Maybe I can shoot this weekend. :grin:

 

[Guest]

As far as the brass is concerned, I was thinking their might be a problem with a few pieces not being concentric, or having different wall thickness, so what I meant was to cull the flier brass from about 5 of the fliers. Then run these 5 through your handloading process again, and see if they group, or if they are all over. If they are all over, it is likely the brass causing the fliers. It is a simple, cheap test to perform, prior to spending a bunch of money on a dial gauge and stand to check concentricity (runout). But if you have different brands of brass, that could well be the problem.

 

[Bigwheels]

Well.Low,& behold I had a decent weather day to chrony the new OAL bullets.I now average right at 2800fps.Thats from a string of 12 rnds. fired through 2 Shooting Chrony's.!st. chrony ave,2808fps. 2nd. chrony ave. 2804fps.Since I really don't trust these chrony's ,thats at least a 50fps. increase from before.More like 100fps increase if you believe the chrony's.They can't both be far off.As for my "flyers".I'm not sure yet.I shot a good group of 10 @ 500yds.All were X rings except for 1 in the 10 ring.Maybe I messed up?Maybe it was mirage?Maybe still haveing flyers?But the bottom line is.If that was a flyer,then it's not as far off as before,& my MV increased 100fps. from an increase of .210" in OAL.
Thanks for all the good input.I'll shoot some more & keep you all posted. :grin:
The strangest thing I noticed is that even with the changes,my 500yd. Zero did NOT change. :?

 

[remingtonman_25_06]

9 out of 10 times I've had a longer OAL, the velocity was always higher then with a shorter OAL. Its weird that your zero did not change even all the way to 500 yards though, I think anyways. But, good job for going out and testing and seeing whats actually going on with your rifle/load.

 

[Bigwheels]

Thats why I don't really trust those chrony's.My Infinity program said that with that change in MV I should have a 5" change in my 500yd. Zero.I also checked the wall thickness oof the case necks on a few cases,& found some to have about .003" difference from 1 side to the other.If I had a few that were that high,or more,that would account for my flyers.I wonder if I should get a neck trimmer? & a concentricity gauge.This rifle is for precision long range shooting after all.

 

[Ol` Joe]

What type of rifle are you useing?
What type of rest? is the rifle setting on the bag at the same place for each shot? Is your grip on the rifle the same each time?
Is your scope free of parellax?
All the screws, rifle and mounts tight?
Do you have wind flags out and how well do you read them?
There are a lot of variables to shooting once you get out 500 yds. The RCBS load program I have shows a 5 mi/hr wind causing a 7.64" wind drift at 500 yds with a Sierra 200 gr MK at 2900 fps. It takes very little misreading of the wind to blow a group at this range. Runout may be a factor but I doubt it is the major cause of your problem.
I don`t see why you question the croney. The fact two of them gave basicly the same reading should give you confidence they are reading right. The BC of your bullet is more of a question then the velocity which is likely within the extreem spread of thee load if you check it further.
The BC changes value depending on velocity. The drop error you are blaming on your croney could be due to a error with the BC instead.
I am not trying to say you are wrong in your assessment of your problem, but only to give you some more possiblities to explore.

 

[Bigwheels]

Thanks Ol Joe.I don't take offense @ other peoples questions.The primary reason I distrust the chrony's is that this is the second time I have been through this with them.Going on the assumption that they were right the first time showing the old load @ 2700fps.The rifle was varified Zero @ 500yds.The new reading of 2800fps. should have netted me a 5" difference in POI.@ 500yds.But the Zero didn't change.The ballistics program is the Sierra Infinity.& I'm useing Sierra 220gr. MatchKings.Sierra has assured me several times that thier data in this program is accurate useing thier bullets.(These are the only ones in the program with different BC's @ different velosities.)As for the rifle.It's a custom Montana Rifle Co. 300WM with #8 contour match barrel,mounted to a Choat Ultimate Tactical stock.I check the mounts,rings,bases,etc every time I take it out of the case.I shoot off a bipod,& have an adjustable rear screw in the base of the stock.As for wind.There was no wind.& As the suspect round was low,& to the right by about 3",I have to assume that either I screwed up,or the round wasn't right in some way.The flyers I had in the last match were over twice that far off,& into the wind.I would have assumed that I screwed these up too,if an experienced shooter hadn't told me they looked funny in flight.I'll be happy if I got them to fly straighter with the change in OAL,& I'll keep testing them as conditions allow,& let you guys know what I find out. :grin: