I am going to do reloading with Varget since I have 10 lbs sitting around.

I have been using it for my .308 heavier bullets but I will using it for 55 grs in my .223.

I have reloaded using both 26.0 grs and 27.0 grs of Varget for the 55 gr Hornaday FMJ-BT and in both cases it worked out fine.  I got as good or slightly better shot groups as I do with my H-335 and CFE 223.  I used Remington 7 1/2 primers.

I will be doing 27.0 grs for this batch of  loads and that of course fills the case up pretty far.

I was wondering if I should switch to CCI 450 magnum primers since the case is compacted full of powder.  I was wondering if I would get more efficient power burn.

Usually I don't see any difference in the performance of a load between the different primers but since this will be a compacted load do you think it make a difference?

Any advice from you more experienced reloaders?  Does a magnum primer make any difference in a compacted load?  Isn't 7 1/2 pretty much a magnum primer anyhow although it is not listed as such?

27gr seems a bit much for 55grfmj...but if it's working for you.

I've never had a ignition or burn problem with Varget...but if you must try, be sure to drop back your charge a bit when switching to magnum primers and work back up looking for over pressure signs.

1) You should not need a magnum primer for Varget.

2) I have read several times, on this forum, that the Rem. 7 1/2 IS equal to a magnum primer. I don't know if that is fact though. I do use the Rem 7 1/2 and have used it with several powders including Varget and have always gotten good results.

If there isn't any unburnt powder, you shouldn't worry about switching primers. The use of magnum primers mainly depends on the type of powder, case capacity, etc.

Varget is a great choice for match loads. Still very popular on the Service Rifle lines. Look at the left column under reloading stuph.
http://njhighpower.com/

The 7.5 primer isn't really a magnum primer, some consider it a bench rest primer, but that really doesn't matter.
What does matter is that you are sensitive to making any changes to loads that are near max.
http://riflemansjournal.blogspot.com/2009/06/primers-small-rifle-primer-study.html

I've always used the CCI #41 primer, recommended for floating firing pin autoloaders, which CCI claims is or should be treated as a small rifle magnum primer load.  I also run Varget behind the 55 gr (Just to minimize powder inventory here, not that it is optimum for 55gr).  I have done the load development starting at 25 up to 27.5gr Varget in 0.5 increments.  I settled on 27.0, which is still fairly hot.

IMO, if you change primers, that is sufficient configuration change, to warrant a cursory workup again.

YMMV

My Varminter seemed to prefer a less hot charge. IIRC, it likes 24 grains for a 55 gr bullet out of a 24" barrel.

A Vmax bullet, for example, has a flat base vs. the FMJBT.  The flat base may have different barrel friction and different barrel sealing characteristics than the FMJBT.  Sometimes we say one 55gr bullet is the same as another 55gr so all is good, but that is not always so.

I am running varget 24.5g with 69g sierra match king and wsm primers.  Good results out of an 18" 1:8 twist

That seems like quite a bit of powder for Varget.  

We tested between four 5.56mm AR's,  and our maximum load that would still maintain accuracy in all of the rifles was 26.0gr.  Perhaps your gun wants more powder,  but it still sounds like quite a bit of varget to drop into a case.

Are you trying to load them heavy to get rid of your powder supply?

I have tested out both 26 gr and 27 gr loads.  I get higher velocity with the 27 gr load without much deterioration in accuracy.  In my 20 inch A2 barrel I get about 3150 FPS with 27 grs and about 2950 with 26 gr.

I shoot at a range with 100-600 yd targets and having the extra velocity is good for the longer distances.

The longer 600 yd range (and somewhat for 300 yd) would do better with a 77 or 80 gr bullet.  Asking the Sierra 69 gr Matchking to do the job at 600 yds is asking for a lot (even without wind). IMHO.

I am a old school type of guy.  Several of my ARs are A1 retros with 1/12 twist.  I try to get as close to M-193 standards as I can.

Varget is a great powder for 223. It burns well in a wide range of temps. It also is in a good spot of the "speed" burn for the .223 and 5.56. I like the powder to fill 90% to slightly over compaction in my rifle loads. So 25-27 grains of Varget in the .223 case is perfect. Although, with range ammo, I'll load a little on the lighter side, to keep from over battering brass. In a small case like a .223, you should not need a mag primer. In a large case like a 7mm Rem Mag using a slow burning powder like Retumbo, R22, or H1000 is where you do want a mag primer. With 67 grains of slow burning powder the mag primer works right. With only 26 grains ov Varget in a .223 case, it is not needed.

Ive loaded several thousand .223 55g with 27 g of Varget. V-max, Ballistic tips, FMJBT and soft points. All with standard primers. Greatest powder ever,