Cooper M21 20 Tac Excessive Jump

[hemi]

A little help gentlemen, if you please.
I am helping a friend out who recently purchased a Cooper Model 21 in 20 Tactical. He purchased the rifle because he has been lusting after my Dakota Predator in 20 Tactical and expected similar accuracy at a more reasonable cost.
Long story short using Dakota/Lapua brass with 35gr Bergers and 24.8gr of Benchmark the Predator groups 5 rounds typically under 1/4".
Using a Stony point/Hornady OAL gage i checked the distance to the lands in the Cooper chamber and found it to be .100" (100 thousandths) further to the lands than my Dakota.
With a case length of 1.750", seating the 35gr Bergers to .010" off the lands would give me a seating depth of the bullet into the neck of only about .040".
Mind you this is a new rifle with no throat erosion. I thought something is wrong with how this rifle was chambered at Cooper.
Anyone with a Cooper chambered in 20 tactical that might be able to offer a little help would be most appreciated.
Hemi

[trotterlg]

All well and good, but is there something wrong with the way it shoots, or do you just think it is bad because it has a long freebore? I am sort of thinking it would be good to shoot it first. Larry

[Gale Johnson]

I have a whole bunch of cooper's, never measured anything as far as ogive to lands. Just shoot the gun, most of mine will shoot well with little or no load development. My friend's tac 20 shoot's like a death ray, haven't messed with it much, 23.5 grains 4198 and a 32 vmax

[hemi]

We broke the barrel in cleaning after every round for the first 25. Then fired three 5 shot groups. Every group would produce 2 or three fliers. A week later we shot another six 5 shot groups with similar results. Groups averaged an inch and a quarter to an inch and a half with the fliers.

My primary question is how much freebore should there be. Using an OAL gage and a dummy round fire formed, i'm getting a measurement of 1.900" from the case head to the ogive with the bullet at the lands. To seat the 35gr Bergers to the lands would give me a seated bullet depth of .030" at the most.

[Old Hawkeye]

Quit being obsessed with "distance to the lands". Who determined the freebore was "excessive"? If you are seating your bullets with only a few thousandths of an inch in the neck your concentricity could be compromised & the reason it's not shooting better groups. Just because a rifle has more freebore than another one doesn't mean it won't shoot as well. Some of mine shoot better with a fairly big bullet "jump" to the lands. Seat your bullets in one caliber in depth & work out a little at a time & see if you can find a "sweet" spot. I consider 1/2 caliber in the neck to be my max OAL. A Cooper that shoots over an inch can usually be attributed to operator error. Let us know how things turn out.

[17varminter]

I've owned 4 cooper in 20 tact and they all varied in freebore. You just have to find a particular load that's a match for that rifle. I sold mine off, I had one beautiful predator and regret selling it.

[Chuck Miller]

I would be concerned with any Cooper shooting 1.25" groups with flyers when using premium components and loaded correctly. Just to verify I would shoot the factory load it was tested with. They don't give you the powder weight but it wouldn't take much to figure it out. You mentioned the components you used in your Dakota, same for the Cooper? I know the 204 is notorious for a long freebore and shooting well with it. In checking my 2 Tac20 customs the freebore in them is close to the Coopers and they both shoot very well.

[TinMan]

Back in 2011, someone on the board here posted the factory loads for Coopers. Might have been Rob. Those records show for a 20 Tactical, 25.0gr of H332 with a 33gr VMAX. No indication of primer or OAL. Hope this helps.

[Jacack]

i have two coopers in 20 tac, both shoot very good with almost everything you put in them. I will measure them tonight for you

[hemi]

Thank you all for chiming in. A little more detail is in order. At the time i loaded the rounds for the cooper i had no measurement of the distance to the lands so i referenced some HSM 20 Tac loaded ammo (Dakota/Lapua brass with 35gr Bergers) that i purchased from I.Q.Metals.com to use when i purchased the Dakota Predator in 20 Tac. This was August of last year and i was just getting started in reloading and the loaded rounds were available and the components i ordered for reloading were trickling in and hard to come by. First time out with the Predator and the HSM ammo i was shooting with my friend who subsequently purchased the Cooper and after dialing in the scope we each shot a five round group @ 100 yds. Looking thru the 6.5-20 x 40mm Leupold both groups looked good so we walked out to the target and both of us stood speechless staring at the groups.......both were one ragged hole. Neither of us had ever shot a rifle so accurate, needless to say i was very happy with the Predator and the HSM ammo.
Back to loading for the Cooper. On the same night i first loaded 50 rounds for the Predator and another 50 for for the Cooper using the same Dakota brass, 35gr Bergers and Benchmark Powder. For the Cooper i loaded ten rounds each starting at a charge weight of 24.0gr and in increments of .2grs. up to 25.0grs. I seated the bullets to the exact same depth as the factory HSM ammo which in the Predator put me about .025" off the lands. The Predator shot all of my rounds well with the best being 24.6gr. The Cooper shot all of the rounds for it about the same with 2 to 3 fliers per 5 round group and group sizes 1.25" to 1.50". That night i measured the Cooper to find the lands and found it to be .100" further out than the Predator. So the jump as loaded for the Cooper was .125"-.130". I started asking questions at that point. I spoke with Cooper customer service yesterday and they responded cautiously and friendly by saying that it was basically a myth from old that a rifle would not shoot accurately with a long jump. Right off they said i could send it back to Cooper and they would check it out and do whatever it took including replacing the barrel to bring the accuracy into specs. Also, i was given the load data using 32gr V-Max bullets and H335 powder to try if i wished before sending it back. I purchased some H335 and 32gr. V-Max's last night and will load 30 rounds tonight and see what happens.
As a sidenote, i am new to reloading but have owned a screw machine shop running multi-spindle machines for 16 years and wear several hats including quality control manager and have measured with certified gages literally 100's of thousands of parts and dimensions. Not bragging mind you just that i DO know how to measure things and the additional .100" of jump in the Cooper stood out as a point of possible issue and the several fliers per group seemed to back up that logic.
Hemi