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Discussion Starter · #1 · (Edited)
Barrel is a 16" Daniels Defense 1:11 5R with SPC II chamber, mid-length, chrome lined: Averaged only 2400 FPS out of three shots with one of the three only netting 2250 FPS. While it still performed well in gel testing (the 120gr MKZ), I had intended to use this for a mid-range hunting load at some point (possibly a mid-range tactical load due to the low expansion velocity) but with these velocities that seems to be throwing in some doubt.

In contrast my dad tested the same 120gr MKZ load (these are loaded by Druid Hill) in his 20" ARP 3R 1:11 and was getting a whopping 2661 FPS which seems fast for a 20" with that load (unless the advertised 2550 FPS is for 16" barrels, doesn't say on their site), but was having cycling issues (yes we are well aware rifle length is the most problematic for this cartridge when it comes to cycling).

Interestingly, he also got a whopping 2650 FPS from 115gr Prvi (which really surprised me), that same load only got 2405 FPS in my previous 16" ARP 3R 1:11 Scout upper and I tested it again (115gr Prvi) in the new Daniels upper I just built and got he same results as with my ARP 16". So both of my 16" barrels netted the same velocity with 115gr Prvi factory, yet a 4" increase in length produced almost 250 FPS more muzzle velocity.

Perhaps my expectations are a bit off, but is it not typical to get around 25~30 FPS per inch with the same barrel (chamber, rifling etc.) just different lengths (comparing the 16" ARP 3R to the 20" ARP 3R)? Because that is NOT what I'm seeing with these heavier loads, they seem to really benefit much more than I'd expect from that extra 4".

Perhaps certain loads are more sensitive when it comes to the heavier bullets than I realize or there are some other factors at play here I'm not aware of affecting muzzle velocity. In contrast I also chronoed my good old Hornady 110gr OTM at 2599 FPS in my 16" Daniels, which is about the same as I got in my 16" ARP. And 110gr VMax (Black) got 2563 FPS in the Daniels, so both of those 110gr loads performed as expected or just a bit above.
 

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Averaged only 2400 FPS out of three shots with one of the three only netting 2250 FPS.
ThELioN70x7, are you making this comparison from 3 rounds? What if that 2250 reading was in error or just one round that had an off powder charge. Drop that reading and your average was just under 2500 fps, more in-line with what you would expect.

I've had multiple 6.8s from 12-inch to 20-inch (2 each of every length except 12- and 14-inch). I found freebore variations between chambers had as much or more affect on mv as barrel length. Depending on the bullet and powder, I've seen as much as 40 fps change per inch of barrel length.

When I had my 20-inch ARP, I found AA2200 often didn't always provide enough with a rifle gas.
 

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Xman is right about freebore. I saw a paper from Hornady one time that showed several "exact" rifles, model and manufacturer where each had its own average velocity. Also each had its own pressure curve. Their were explaining about the Superformance powder when it came out and how people were saying the factory ammo was not giving them the velocity on the box. The paper stated that freebore was different on each rifle and that caused the greatest affect, also headspace and internal bore dimensions were secondary.
 

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Discussion Starter · #4 ·
Correction on the Prvi 115gr, average was 2575 for my pops 20" ARP and 2663 FPS for the 120gr MKZ loaded by DHA, both were 7 shot strings each.

So Prvi netted 160 fps from 4" more barrel (remember with Prvi I got 2400 flat from both my 16" ARP 3R and my 16" DD 5R, so that load really likes long barrels as there was no difference between the two 16s).

And I got 2663 FPS average from DHAs 110gr Nossler on my DD 16", it just was a no go due to cycling issues so I swapped it out for VMax as DHA didn't have an ETA on a new batch with different powder.

I would agree I should have shot a 7 shot string as I normally do for the MKZ load, but after the first three were so low I wondered if I had developed a leak somewhere so I went back to 110 gr OTM to check mv and forgot to go back and do another string with the 120gr MKZ.

Next time I'm out I'll shoot a string of 7 for the MKZ to see what the average is, but I'm not expecting much change. Seems this load does not like the combination of 16" and SPC II chamber even with 1:11 twist and 5R odd rifling, it would make sense the combination of barrel length and free bore are the likely factors.

The MKZ 120 is a long load, they literally wouldn't fit in my dad's DH 25rd mags but fit fine in my ASC. Haven't measured OAL but I can visually see OAL is markedly longer than OTM, VMax or WC 95gr TTSX.

I don't believe the difference in freebore was significant between SPC II and ARP was it?
 

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Discussion Starter · #5 · (Edited)
BTW the three shots were 2395, 2281 and 2361. Average works out to 2345. Even discounting the low ball middle shot, assuming velocity remains in that range that's weak compared to several of the SAAMI spec factory loads and this is supposed to be a hot load (aka a NATO or +P).

I'd accept 2450 as good for monolithic 120gr from a 16", but just under 2400 seems pretty low. I could try shutting for gas flow just in case there's early unlocking but ejection doesn't seem to indicate abnormal carrier speed (between 330 and 4). No signs of anything abnormal on the case either.
 

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The reamers that produce all the 6.8mm barrels are not all identical. Plus there is reamer wear which I've been told that a 0.001" of wear can make a 0.017" difference in freebore. I've seen 0.050" differences in freebore between the smallest and largest freebores of the many 6.8 barrels I've had. I've had 0.090" difference in freebore between two 300 BO barrels made from the same company.
 
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Discussion Starter · #7 · (Edited)
I don't believe the issues with the reamers wearing apply to DD barrels because they are cold hammer forged around a mandrel. The mandrels the barrel is formed around are what determine the free bore dimensions, typically they are tungsten. The tooling life is measured not in thousands but millions.

Considering how low volume 6.8 is relative to 5.56 and the fact that Daniels recently invested yet again in new tooling to move to 1:11 twist from their original 1:10, I'd wager the chamber dimensions are extremely good.

The entire chamber is hammer forged along with the throat and bore. And with the modern electro plating process pioneered by Boeing which more than doubles the service life of chrome lined barrels over the much less durable and less uniform chemical etching process (aka GI spec), I don't believe that the plating technique has any negative impact.

So unless it's a mfg defect, I'm starting to think it's a combination of the particular iteration of SPC II they used for the chamber and the 16" barrel length, probably mostly the barrel length given there was also a pretty significant difference in MV in Prvi Partisan 115gr between our two barrels. And I also had tested the same Prvi load in my 16" ARP barrel and netted 2405 FPS, so both 16" barrels I've used shot Prvi 160 FPS slower than the 20" regardless of rifling, chamber or plating types.
 

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A lot of hammer-forged barrels are chambered in a separate operation with a standard chamber reamer. I am curious now what process DD uses. If they use the SPC II reamer with the 0.100 freebore, they will generally be slower than Bison and ARP barrels which have shorter freebores. Of course, there is significant barrel-to-barrel variation anyway.
 

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I think I was at around 2450 on my 16 inch Bison with AA2200. Never really pushed the load as I planned to switch to 105's
 

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Discussion Starter · #10 · (Edited)
A lot of hammer-forged barrels are chambered in a separate operation with a standard chamber reamer. I am curious now what process DD uses. If they use the SPC II reamer with the 0.100 freebore, they will generally be slower than Bison and ARP barrels which have shorter freebores. Of course, there is significant barrel-to-barrel variation anyway.
I spoke with Daniels on this and the entire chamber is hammer forged along with the bore on a single mandrel. They claimed this process resulted in the greatest uniformity. Sure, the blank is reamed prior to the cold hammer forging process so the mandrel can be inserted into the blank, however it is then hammed into shape around the mandrel (about 50k psi) so the final dimensions are determined by the mandrel itself: Daniel Defense Barrel-Making Process - YouTube
 

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2400 fps with the 120mkz is 1400 at 500 yards . 120 mkz expands down to 1400 . I don't know about you but I don't plan on shooting at anything breathing that far out unless it is try to shoot me . I would be more concerned about how accurate it shoots them .

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Discussion Starter · #12 · (Edited)
Touché, I guess I did not consider the effective range even at the reduced velocity. Interestingly drag causes much higher losses at the higher velocities. Some times a lower muzzle velocity is not as "bad" as it seems other than some added drop. Although, I did have to check cause that didn't come to mind that this load does expand down that low, but sure enough, assuming Hornady's BC is reasonably close, about 450 to 500 yards expansion from a 16" barrel.

The extra 250 FPS my dad netted buys him another 100 yards (expansion out to 600), but again as mentioned, under real world field conditions that's a pretty long shot for 6.8 SPC, there are better tool at that range. I suppose despite my hopes for 2450+ this isn't bad assuming an actual 7-shot string yields about 2400 average.
 

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Touché, I guess I did not consider the effective range even at the reduced velocity. Interestingly drag causes much higher losses at the higher velocities. Some times a lower muzzle velocity is not has "bad" as it seems other than some added drop. Although, I did have to check cause that didn't come to mind that this load does expand down that load, but sure enough, assuming Hornady's BC is reasonably close, about 450 to 500 yards expansion from a 16" barrel.

The extra 250 FPS my dad netted buys him another 100 yards (expansion out to 600), but again as mentioned, under real world field conditions that's a pretty long shot for 6.8 SPC, there are better tool at that range. I suppose despite my hopes for 2500 this isn't bad assuming an actual 7-shot string yields about 2400 average.
My 12.5"ARP gives me 2470 ( hand loads ) 105 CBB the same bullet is going 2740 out of my 18" ARP ,easy to remember the numbers . The performance on game is identical between the two . In all actuality the 120 CBB might be the better choice past 200 yards maybe 150 with 12.5" (at least on paper ). The 105s extra velocity helps it expand more at short range but after a football field or two the speed difference has narrowed and the 120 expands a fraction more and maintains more energy . Sounds just the opposite than you might think , faster 105 better up close slower 120 better farther out . My guns shoot 105s so well and the performance is great so I'm going to stick with them .


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Both the 105 and 120 MKZ ammo is loaded to what folks here have been loading for over 4 years now.
I intentionally had DHA load 2.285 COAL (site has a disclaimer to this fact) to duplicate what handloaders are using.
The 120 is loaded to 27.5 grains of AA2200, the signature loads everyone has been using.
The 105 at 29.5
The pressure trace data shows that to be right around 57000 PSI.
Anything higher would not be good considering freebore differences in barrels.

As Xman said a 3 shot assessment is really not a good indication.
This is a first run of ammo. We want feedback, I can adjust anything on the next (only 20 boxes left in this one) if the need to do so surfaces.

As to the 2.285 COAL this was intentional to keep the pressures up and increase accuracy with less jump to the lands. SSA used to load 130 Bergers at 2.30.
I have not tested in DH mags, but have tested in PRI, CPD and ASC.

Which crono do you have? Was is sunny? Cloudy? Mix of both? This also alters readings.

We are looking for more feedback so please continue.
 

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Both the 105 and 120 MKZ ammo is loaded to what folks here have been loading for over 4 years now.
I intentionally had DHA load 2.285 COAL (site has a disclaimer to this fact) to duplicate what handloaders are using.
The 120 is loaded to 27.5 grains of AA2200, the signature loads everyone has been using.
The 105 at 29.5
The pressure trace data shows that to be right around 57000 PSI.
Anything higher would not be good considering freebore differences in barrels.

As Xman said a 3 shot assessment is really not a good indication.
This is a first run of ammo. We want feedback, I can adjust anything on the next (only 20 boxes left in this one) if the need to do so surfaces.

As to the 2.285 COAL this was intentional to keep the pressures up and increase accuracy with less jump to the lands. SSA used to load 130 Bergers at 2.30.
I have not tested in DH mags, but have tested in PRI, CPD and ASC.

Which crono do you have? Was is sunny? Cloudy? Mix of both? This also alters readings.

We are looking for more feedback so please continue.
I tried a box of both the DHA 105 and the 120 out of my 16” scout ARP 5r. I did not test velocity, only 3 shot grouping. That will change the next range trip. The 105 grouped right with my hand loads of 29g of 2200 at 1.2 MOA. The 120s didn’t fair as well, with the group measuring 2.5moa.
 

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What barrel are you using ? What size group do you get with Hornady SST 120 .or other factory loads ?

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Roseaukaine the CBB is reported to be loaded with 2200 ,which you said in a previous post your gun doesn't digest well . I saw In this post you named the powder you get 1.2 " with as 2200 but in a previous post you said it was h322 . Is it possible you have the two mixed up ?

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Roseaukaine the CBB is reported to be loaded with 2200 ,which you said in a previous post your gun doesn't digest well . I saw In this post you named the powder you get 1.2 " with as 2200 but in a previous post you said it was h322 . Is it possible you have the two mixed up ?

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I have 2 loads for the CBB 105. One is 29g of 2200, the other is H322. 2200 is faster but the H322 is more temp stable And slightly more accurate.
The 120s I’m having issues with achieving acceptable accuracy with velocity.

Im located where the temps can vary considerably so I’d prefer a more temp stable powder.
 

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What barrel are you using ? What size group do you get with Hornady SST 120 .or other factory loads ?

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Factory hornandy SST doesn’t group well out my 16” either. I have a few hundred of these projectiles but haven’t tried loading them yet.
 
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